Revert "feat: enforce email null when deleted is set" (#10682)

Reverts Unleash/unleash#10680

SCIM protocol requires us to keep the email stored, so this constraint
doesn't hold.

src/lib/features/instance-stats/getLicensedUsers.e2e.test.ts

@@ -16,7 +16,7 @@ const mockUser = (deletedDaysAgo: number | null, uniqueId: number) => {
             ? new Date(Date.now() - deletedDaysAgo * 24 * 60 * 60 * 1000)
             : null;
     return {
-        email: deletedAt === null ? `${uniqueId}.user@example.com` : null,
+        email: `${uniqueId}.user@example.com`,
         email_hash: `${uniqueId}.user@example.com`,
         deleted_at: deletedAt,
     };

src/lib/features/users/user-store.ts

@@ -352,13 +352,4 @@ export class UserStore implements IUserStore {
 
         return firstInstanceUser ? firstInstanceUser.created_at : null;
     }
-
-    // this is temporary to find out how many cases we have
-    async findDeletedUsersWithEmail(): Promise<User[]> {
-        return this.db(TABLE)
-            .select('*')
-            .whereNotNull('deleted_at')
-            .andWhereRaw('length(email) > 0')
-            .then((rows) => rows.map(rowToUser));
-    }
 }

src/migrations/20250922151744-amend-deleted-at.js

@@ -1,25 +0,0 @@
-
-exports.up = (db, callback) => {
-    db.runSql(
-        `
-        UPDATE users
-        SET deleted_at = NULL
-        WHERE deleted_at IS NOT NULL and length(email) > 0;
-
-        ALTER TABLE users
-        ADD CONSTRAINT deleted_at_requires_email_null
-        CHECK (deleted_at IS NULL OR email IS NULL);
-        `,
-        callback,
-    );
-};
-
-exports.down = (db, callback) => {
-    db.runSql(
-        `
-        ALTER TABLE users
-        DROP CONSTRAINT deleted_at_requires_email_null;
-        `,
-        callback,
-    );
-};