[AC-2522] Remove collection enhancements opt-in (#9283)

* Remove FlexibleCollectionsMigration feature flag and code

* Remove api method

apps/web/src/app/admin-console/organizations/settings/account.component.html

@@ -50,29 +50,6 @@
       {{ "rotateApiKey" | i18n }}
     </button>
   </ng-container>
-  <form
-    *ngIf="
-      org && !loading && !org.flexibleCollections && (flexibleCollectionsMigrationEnabled$ | async)
-    "
-  >
-    <h1 bitTypography="h1" class="tw-mt-16 tw-pb-2.5">
-      {{ "collectionManagement" | i18n }}
-    </h1>
-    <p>
-      {{ "collectionEnhancementsDesc" | i18n }}
-      <a href="https://bitwarden.com/help/collection-management" target="_blank" rel="noreferrer">
-        {{ "collectionEnhancementsLearnMore" | i18n }}
-      </a>
-    </p>
-    <button
-      type="button"
-      bitButton
-      buttonType="primary"
-      (click)="showConfirmCollectionEnhancementsDialog()"
-    >
-      {{ "enable" | i18n }}
-    </button>
-  </form>
   <form
     *ngIf="org && !loading && org.flexibleCollections"
     [bitSubmit]="submitCollectionManagement"