cleanup: remove no longer used code 🔥🔥🔥

The code for handling device availability has been disabled for a long time,
plus it's ill named since it represents 2 abstractions: lack of permissions and
lack of devices.

Time for it to rest in the git graveyard.

conference.js

                 && APP.UI.notifyInitiallyMuted();
         });
 
-        room.on(
-            JitsiConferenceEvents.AVAILABLE_DEVICES_CHANGED,
-            (id, devices) => {
-                APP.UI.updateDevicesAvailability(id, devices);
-            }
-        );
-
         room.on(
             JitsiConferenceEvents.DATA_CHANNEL_OPENED, () => {
                 APP.store.dispatch(dataChannelOpened());

css/_videolayout_default.scss

     object-fit: cover;
 }
 
-.noMic {
-    position: absolute;
-    border-radius: 8px;
-    z-index: $zindex1;
-    width: 100%;
-    height: 100%;
-    background-image: url("../images/noMic.png");
-    background-color: #000;
-    background-repeat: no-repeat;
-    background-position: center;
-}
-
-.noVideo {
-    position: absolute;
-    border-radius: 8px;
-    z-index: $zindex1;
-    width: 100%;
-    height: 100%;
-    background-image: url("../images/noVideo.png");
-    background-color: #000;
-    background-repeat: no-repeat;
-    background-position: center;
-}
-
 .videoMessageFilter {
     -webkit-filter: grayscale(.5) opacity(0.8);
     filter: grayscale(.5) opacity(0.8);

modules/UI/UI.js

     } else {
         // Initialize recording mode UI.
         if (config.iAmRecorder) {
-            VideoLayout.enableDeviceAvailabilityIcons(
-                APP.conference.getMyUserId(), false);
-
             // in case of iAmSipGateway keep local video visible
             if (!config.iAmSipGateway) {
                 VideoLayout.setLocalVideoVisible(false);

modules/UI/videolayout/SmallVideo.js

     return this.$container.is(':visible');
 };
 
-/**
- * Enables / disables the device availability icons for this small video.
- * @param {enable} set to {true} to enable and {false} to disable
- */
-SmallVideo.prototype.enableDeviceAvailabilityIcons = function(enable) {
-    if (typeof enable === 'undefined') {
-        return;
-    }
-
-    this.deviceAvailabilityIconsEnabled = enable;
-};
-
-/**
- * Sets the device "non" availability icons.
- * @param devices the devices, which will be checked for availability
- */
-SmallVideo.prototype.setDeviceAvailabilityIcons = function(devices) {
-    if (!this.deviceAvailabilityIconsEnabled) {
-        return;
-    }
-
-    if (!this.container) {
-        return;
-    }
-
-    const noMic = this.$container.find('.noMic');
-    const noVideo = this.$container.find('.noVideo');
-
-    noMic.remove();
-    noVideo.remove();
-    if (!devices.audio) {
-        this.container.appendChild(
-            document.createElement('div')).setAttribute('class', 'noMic');
-    }
-
-    if (!devices.video) {
-        this.container.appendChild(
-            document.createElement('div')).setAttribute('class', 'noVideo');
-    }
-
-    if (!devices.audio && !devices.video) {
-        noMic.css('background-position', '75%');
-        noVideo.css('background-position', '25%');
-        noVideo.css('background-color', 'transparent');
-    }
-};
-
 /**
  * Sets the type of the video displayed by this instance.
  * Note that this is a string without clearly defined or checked values, and

modules/UI/videolayout/VideoLayout.js

         video.setDeviceAvailabilityIcons(devices);
     },
 
-    /**
-     * Enables/disables device availability icons for the given participant id.
-     * The default value is {true}.
-     * @param id the identifier of the participant
-     * @param enable {true} to enable device availability icons
-     */
-    enableDeviceAvailabilityIcons(id, enable) {
-        let video;
-
-        if (APP.conference.isLocalId(id)) {
-            video = localVideoThumbnail;
-        } else {
-            video = remoteVideos[id];
-        }
-
-        if (video) {
-            video.enableDeviceAvailabilityIcons(enable);
-        }
-    },
-
     /**
      * Shows/hides local video.
      * @param {boolean} true to make the local video visible, false - otherwise