fix(conference) remove no longer needed code

There is no need for setting the availability of desktop sharing anymore. It can
now be detected on the spot.

The reson for the previous code was that way back when browser extensions were
needed, it was possible to start a conference without desktopo sharing support
and get it afterwards. This is no longer the case.

react/features/base/conference/actionTypes.js

@@ -140,18 +140,6 @@ export const P2P_STATUS_CHANGED = 'P2P_STATUS_CHANGED';
  */
 export const SEND_TONES = 'SEND_TONES';
 
-/**
- * The type of (redux) action which sets the desktop sharing enabled flag for
- * the current conference.
- *
- * {
- *     type: SET_DESKTOP_SHARING_ENABLED,
- *     desktopSharingEnabled: boolean
- * }
- */
-export const SET_DESKTOP_SHARING_ENABLED
-    = 'SET_DESKTOP_SHARING_ENABLED';
-
 /**
  * The type of (redux) action which updates the current known status of the
  * Follow Me feature.

react/features/base/conference/actions.js

@@ -43,7 +43,6 @@ import {
     LOCK_STATE_CHANGED,
     P2P_STATUS_CHANGED,
     SEND_TONES,
-    SET_DESKTOP_SHARING_ENABLED,
     SET_FOLLOW_ME,
     SET_PASSWORD,
     SET_PASSWORD_FAILED,
@@ -573,22 +572,6 @@ export function sendTones(tones: string, duration: number, pause: number) {
     };
 }
 
-/**
- * Sets the flag for indicating if desktop sharing is enabled.
- *
- * @param {boolean} desktopSharingEnabled - True if desktop sharing is enabled.
- * @returns {{
- *     type: SET_DESKTOP_SHARING_ENABLED,
- *     desktopSharingEnabled: boolean
- * }}
- */
-export function setDesktopSharingEnabled(desktopSharingEnabled: boolean) {
-    return {
-        type: SET_DESKTOP_SHARING_ENABLED,
-        desktopSharingEnabled
-    };
-}
-
 /**
  * Enables or disables the Follow Me feature.
  *

react/features/base/conference/reducer.js

@@ -16,7 +16,6 @@ import {
     CONFERENCE_WILL_LEAVE,
     LOCK_STATE_CHANGED,
     P2P_STATUS_CHANGED,
-    SET_DESKTOP_SHARING_ENABLED,
     SET_FOLLOW_ME,
     SET_PASSWORD,
     SET_PENDING_SUBJECT_CHANGE,
@@ -76,9 +75,6 @@ ReducerRegistry.register(
         case P2P_STATUS_CHANGED:
             return _p2pStatusChanged(state, action);
 
-        case SET_DESKTOP_SHARING_ENABLED:
-            return _setDesktopSharingEnabled(state, action);
-
         case SET_FOLLOW_ME:
             return set(state, 'followMeEnabled', action.enabled);
 
@@ -343,21 +339,6 @@ function _p2pStatusChanged(state, action) {
     return set(state, 'p2p', action.p2p);
 }
 
-/**
- * Reduces a specific Redux action SET_DESKTOP_SHARING_ENABLED of the feature
- * base/conference.
- *
- * @param {Object} state - The Redux state of the feature base/conference.
- * @param {Action} action - The Redux action SET_DESKTOP_SHARING_ENABLED to
- * reduce.
- * @private
- * @returns {Object} The new state of the feature base/conference after the
- * reduction of the specified action.
- */
-function _setDesktopSharingEnabled(state, action) {
-    return set(state, 'desktopSharingEnabled', action.desktopSharingEnabled);
-}
-
 /**
  * Reduces a specific Redux action SET_PASSWORD of the feature base/conference.
  *