chore: remove custom strategy deprecation warnings from release tempates (#10929)

Remove two more deprecations for custom stategies

frontend/src/component/feature/FeatureStrategy/FeatureStrategyForm/FeatureStrategyForm.tsx

@@ -10,7 +10,6 @@ import {
     Box,
     Divider,
     Typography,
-    Link,
 } from '@mui/material';
 import type {
     IFeatureStrategy,
@@ -43,7 +42,7 @@ import { useHasProjectEnvironmentAccess } from 'hooks/useHasAccess';
 import { FeatureStrategyTitle } from './FeatureStrategyTitle/FeatureStrategyTitle.tsx';
 import { FeatureStrategyEnabledDisabled } from './FeatureStrategyEnabledDisabled/FeatureStrategyEnabledDisabled.tsx';
 import { usePlausibleTracker } from 'hooks/usePlausibleTracker';
-import { BuiltInStrategies, formatStrategyName } from 'utils/strategyNames';
+import { formatStrategyName } from 'utils/strategyNames';
 import { Badge } from 'component/common/Badge/Badge';
 import { UpgradeChangeRequests } from '../../FeatureView/FeatureOverview/FeatureOverviewEnvironments/FeatureOverviewEnvironment/UpgradeChangeRequests/UpgradeChangeRequests.tsx';
 import { ConstraintSeparator } from 'component/common/ConstraintsList/ConstraintSeparator/ConstraintSeparator';
@@ -343,29 +342,6 @@ export const FeatureStrategyForm = ({
                         />
                     }
                 />
-
-                <ConditionallyRender
-                    condition={
-                        !BuiltInStrategies.includes(strategy.name || 'default')
-                    }
-                    show={
-                        <Alert severity='warning'>
-                            Custom strategies are deprecated. We recommend not
-                            adding them to any flags going forward and using the
-                            predefined strategies like Gradual rollout with{' '}
-                            <Link
-                                href={
-                                    'https://docs.getunleash.io/reference/activation-strategies#constraints'
-                                }
-                                target='_blank'
-                                variant='body2'
-                            >
-                                constraints
-                            </Link>{' '}
-                            instead.
-                        </Alert>
-                    }
-                />
             </StyledAlertBox>
 
             <StyledTabs value={tab} onChange={handleChange}>

frontend/src/component/releases/ReleasePlanTemplate/TemplateForm/MilestoneStrategy/ReleasePlanTemplateAddStrategyForm.tsx

@@ -3,7 +3,6 @@ import {
     Button,
     styled,
     Alert,
-    Link,
     Tab,
     Tabs,
     Typography,
@@ -14,7 +13,7 @@ import FormTemplate from 'component/common/FormTemplate/FormTemplate';
 import type { IReleasePlanMilestoneStrategy } from 'interfaces/releasePlans';
 import type { ISegment } from 'interfaces/segment';
 import { useEffect, useState } from 'react';
-import { BuiltInStrategies, formatStrategyName } from 'utils/strategyNames';
+import { formatStrategyName } from 'utils/strategyNames';
 import { useStrategy } from 'hooks/api/getters/useStrategy/useStrategy';
 import { useFormErrors } from 'hooks/useFormErrors';
 import produce from 'immer';
@@ -66,15 +65,6 @@ const StyledTitle = styled('h1')(({ theme }) => ({
     paddingBottom: theme.spacing(2),
 }));
 
-const StyledAlertBox = styled(Box)(({ theme }) => ({
-    paddingLeft: theme.spacing(6),
-    paddingRight: theme.spacing(6),
-    '& > *': {
-        marginTop: theme.spacing(2),
-        marginBottom: theme.spacing(2),
-    },
-}));
-
 const StyledTabs = styled(Tabs)(({ theme }) => ({
     borderTop: `1px solid ${theme.palette.divider}`,
     borderBottom: `1px solid ${theme.palette.divider}`,
@@ -245,27 +235,6 @@ export const ReleasePlanTemplateAddStrategyForm = ({
                     )}
                 </StyledTitle>
             </StyledHeaderBox>
-            {!BuiltInStrategies.includes(
-                strategy.strategyName || 'default',
-            ) && (
-                <StyledAlertBox>
-                    <Alert severity='warning'>
-                        Custom strategies are deprecated. We recommend not
-                        adding them to any templates going forward and using the
-                        predefined strategies like Gradual rollout with{' '}
-                        <Link
-                            href={
-                                'https://docs.getunleash.io/reference/activation-strategies#constraints'
-                            }
-                            target='_blank'
-                            variant='body2'
-                        >
-                            constraints
-                        </Link>{' '}
-                        instead.
-                    </Alert>
-                </StyledAlertBox>
-            )}
             <StyledTabs value={activeTab} onChange={handleChange}>
                 <StyledTab label='General' />
                 <Tab