Take encrypted message search out of labs

Fixes https://github.com/vector-im/riot-web/issues/13262

This is part of the cross-signing shipping master plan. Known issues relating to this feature are:
* https://github.com/vector-im/riot-web/issues/12896
* https://github.com/vector-im/riot-web/issues/12385
* https://github.com/vector-im/riot-web/issues/11831
* https://github.com/vector-im/riot-web/issues/11155

In theory, these are issues we're comfortable with shipping as we're already enabling it by default. This just makes it easier on everyone by removing the flag (making it still enabled by default).

src/components/views/settings/tabs/user/SecurityUserSettingsTab.js

@@ -254,15 +254,12 @@ export default class SecurityUserSettingsTab extends React.Component {
             </div>
         );
 
-        let eventIndex;
-        if (SettingsStore.isFeatureEnabled("feature_event_indexing")) {
-            eventIndex = (
+        let eventIndex = (
             <div className="mx_SettingsTab_section">
                 <span className="mx_SettingsTab_subheading">{_t("Message search")}</span>
                 <EventIndexPanel />
             </div>
         );
-        }
 
         // XXX: There's no such panel in the current cross-signing designs, but
         // it's useful to have for testing the feature. If there's no interest

src/indexing/EventIndexPeg.js

@@ -37,10 +37,6 @@ class EventIndexPeg {
      * EventIndex was successfully initialized, false otherwise.
      */
     async init() {
-        if (!SettingsStore.isFeatureEnabled("feature_event_indexing")) {
-            return false;
-        }
-
         const indexManager = PlatformPeg.get().getEventIndexingManager();
         if (!indexManager) {
             console.log("EventIndex: Platform doesn't support event indexing, not initializing.");

src/settings/Settings.js

@@ -152,12 +152,6 @@ export const SETTINGS = {
         supportedLevels: ['device', 'config'], // we shouldn't use LEVELS_FEATURE for non-features, so copy it here.
         default: true,
     },
-    "feature_event_indexing": {
-        isFeature: true,
-        supportedLevels: LEVELS_FEATURE,
-        displayName: _td("Enable local event indexing and E2EE search (requires restart)"),
-        default: false,
-    },
     "feature_bridge_state": {
         isFeature: true,
         supportedLevels: LEVELS_FEATURE,