Remove path aliases for the self folder from configs (#4825)

# Description of Changes
Remove path aliases from self folder (e.g. remove `@core` from
`tsconfig.core.json`). It's not necessary and using it means that it's
impossible for the other folders to override the behaviour. The only
reason we should currently be using `@core` is in `proprietary` where we
need to explicitly import the `core` version of the thing we're
overriding so that we can re-expose or use the objects.

frontend/tsconfig.core.json

@@ -4,8 +4,7 @@
     "paths": {
       "@app/*": [
         "src/core/*"
-      ],
-      "@core/*": ["src/core/*"]
+      ]
     }
   },
   "exclude": [

frontend/tsconfig.proprietary.json

@@ -6,7 +6,6 @@
         "src/proprietary/*",
         "src/core/*"
       ],
-      "@proprietary/*": ["src/proprietary/*"],
       "@core/*": ["src/core/*"]
     }
   }