Remove impossible labs feature: sending hidden read receipts

This claims it requires a compatible homeserver, but that does not exist and hasn't for years. Let's just remove the option to stop giving people false hope.

Once notifications are decoupled from read receipts, this sort of thing should be more possible.

src/components/structures/TimelinePanel.js

@@ -716,19 +716,17 @@ class TimelinePanel extends React.Component {
             this.lastRMSentEventId = this.state.readMarkerEventId;
 
             const roomId = this.props.timelineSet.room.roomId;
-            const hiddenRR = !SettingsStore.getValue("sendReadReceipts", roomId);
 
             debuglog('TimelinePanel: Sending Read Markers for ',
                 this.props.timelineSet.room.roomId,
                 'rm', this.state.readMarkerEventId,
                 lastReadEvent ? 'rr ' + lastReadEvent.getId() : '',
-                ' hidden:' + hiddenRR,
             );
             MatrixClientPeg.get().setRoomReadMarkers(
                 this.props.timelineSet.room.roomId,
                 this.state.readMarkerEventId,
                 lastReadEvent, // Could be null, in which case no RR is sent
-                {hidden: hiddenRR},
+                {},
             ).catch((e) => {
                 // /read_markers API is not implemented on this HS, fallback to just RR
                 if (e.errcode === 'M_UNRECOGNIZED' && lastReadEvent) {

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

@@ -67,7 +67,6 @@ export default class LabsUserSettingsTab extends React.Component {
                     <SettingsFlag name={"enableWidgetScreenshots"} level={SettingLevel.ACCOUNT} />
                     <SettingsFlag name={"showHiddenEventsInTimeline"} level={SettingLevel.DEVICE} />
                     <SettingsFlag name={"lowBandwidth"} level={SettingLevel.DEVICE} />
-                    <SettingsFlag name={"sendReadReceipts"} level={SettingLevel.ACCOUNT} />
                     <SettingsFlag name={"advancedRoomListLogging"} level={SettingLevel.DEVICE} />
                 </div>
             </div>

src/i18n/strings/en_EN.json

@@ -820,7 +820,6 @@
     "Show hidden events in timeline": "Show hidden events in timeline",
     "Low bandwidth mode": "Low bandwidth mode",
     "Allow fallback call assist server turn.matrix.org when your homeserver does not offer one (your IP address would be shared during a call)": "Allow fallback call assist server turn.matrix.org when your homeserver does not offer one (your IP address would be shared during a call)",
-    "Send read receipts for messages (requires compatible homeserver to disable)": "Send read receipts for messages (requires compatible homeserver to disable)",
     "Show previews/thumbnails for images": "Show previews/thumbnails for images",
     "Enable message search in encrypted rooms": "Enable message search in encrypted rooms",
     "How fast should messages be downloaded.": "How fast should messages be downloaded.",

src/settings/Settings.ts

@@ -564,13 +564,6 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         // This is a tri-state value, where `null` means "prompt the user".
         default: null,
     },
-    "sendReadReceipts": {
-        supportedLevels: LEVELS_ROOM_SETTINGS,
-        displayName: _td(
-            "Send read receipts for messages (requires compatible homeserver to disable)",
-        ),
-        default: true,
-    },
     "showImages": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td("Show previews/thumbnails for images"),