compose: Remove @topic from autocomplete, for now

It turns out that server support for this hasn't landed yet. Once it
has, we'll know what feature level to condition on.

src/autocomplete/PeopleAutocomplete.js

@@ -67,7 +67,14 @@ export default function PeopleAutocomplete(props: Props): Node {
   );
 
   const filteredUserGroups = getAutocompleteUserGroupSuggestions(userGroups, filter);
-  const wildcardMentionsForQuery = getWildcardMentionsForQuery(filter, destinationNarrow, _);
+  const wildcardMentionsForQuery = getWildcardMentionsForQuery(
+    filter,
+    destinationNarrow,
+    // TODO condition on feature level, once we know which one:
+    //   https://chat.zulip.org/#narrow/stream/378-api-design/topic/.40topic/near/1669340
+    false,
+    _,
+  );
   const filteredUsers = getAutocompleteSuggestion(users, filter, ownUserId, mutedUsers);
 
   if (filteredUserGroups.length + filteredUsers.length === 0) {

src/autocomplete/WildcardMentionItem.js

@@ -85,6 +85,7 @@ const descriptionOf = (
 export const getWildcardMentionsForQuery = (
   query: string,
   destinationNarrow: Narrow,
+  topicMentionSupported: boolean,
   _: GetText,
 ): $ReadOnlyArray<WildcardMentionType> => {
   const queryMatchesWildcard = (type: WildcardMentionType): boolean =>
@@ -112,7 +113,11 @@ export const getWildcardMentionsForQuery = (
   }
 
   // Then show @-topic if it applies.
-  if (isStreamOrTopicNarrow(destinationNarrow) && queryMatchesWildcard(WildcardMentionType.Topic)) {
+  if (
+    topicMentionSupported
+    && isStreamOrTopicNarrow(destinationNarrow)
+    && queryMatchesWildcard(WildcardMentionType.Topic)
+  ) {
     results.push(WildcardMentionType.Topic);
   }