Deprecate share email thread (#9319)

## Context

Following this https://github.com/twentyhq/twenty/issues/4199
This has not been fully implemented, after 5months of dead code I'm
removing the feature for the time being until we re-prioritise the
feature (unlikely during these next 6 months) to keep the codebase a bit
cleaner (no need to maintain dead features)

Feel free to reopen / revert this PR once feature is ready

## Test
locally after importing emails

packages/twenty-front/src/modules/activities/emails/graphql/operation-signatures/factories/fetchAllThreadMessagesOperationSignatureFactory.ts

@@ -2,13 +2,7 @@ import { CoreObjectNameSingular } from '@/object-metadata/types/CoreObjectNameSi
 import { RecordGqlOperationSignatureFactory } from '@/object-record/graphql/types/RecordGqlOperationSignatureFactory';
 
 export const fetchAllThreadMessagesOperationSignatureFactory: RecordGqlOperationSignatureFactory =
-  ({
-    messageThreadId,
-    isSubscribersEnabled,
-  }: {
-    messageThreadId: string;
-    isSubscribersEnabled: boolean;
-  }) => ({
+  ({ messageThreadId }: { messageThreadId: string }) => ({
     objectNameSingular: CoreObjectNameSingular.Message,
     variables: {
       filter: {
@@ -33,15 +27,6 @@ export const fetchAllThreadMessagesOperationSignatureFactory: RecordGqlOperation
       receivedAt: true,
       messageThread: {
         id: true,
-        subscribers: isSubscribersEnabled
-          ? {
-              workspaceMember: {
-                id: true,
-                name: true,
-                avatarUrl: true,
-              },
-            }
-          : undefined,
       },
       messageParticipants: {
         id: true,