Removes disableDesktopSharing option.

doc/API.md

 *  ```JitsiMeetJS.init(options)``` - this method initialized Jitsi Meet API.
 The ```options``` parameter is JS object with the following properties:
     - `useIPv6` - boolean property
-    - `disableDesktopSharing` - Boolean. When set to true disables desktop sharing on all browsers. 
     - `desktopSharingChromeExtId` - The ID of the jidesha extension for Chrome. Example: 'mbocklcggfhnbahlnepmldehdhpjfcjp'
     - `desktopSharingChromeDisabled` - Boolean. Whether desktop sharing should be disabled on Chrome. Example: false.
     - `desktopSharingChromeSources` - Array of strings with the media sources to use when using screen sharing with the Chrome extension. Example: ['screen', 'window']

modules/RTC/ScreenObtainer.js

      * (this.obtainStream).
      *
      * @param {object} options
-     * @param {boolean} [options.disableDesktopSharing]
      * @param {boolean} [options.desktopSharingChromeDisabled]
      * @param {boolean} [options.desktopSharingChromeExtId]
      * @param {boolean} [options.desktopSharingFirefoxDisabled]
      * @param {Function} gum GUM method
      */
     init(options = {
-        disableDesktopSharing: false,
         desktopSharingChromeDisabled: false,
         desktopSharingChromeExtId: null,
         desktopSharingFirefoxDisabled: false
         this.options = options;
         gumFunction = gum;
 
-        this.obtainStream
-            = this.options.disableDesktopSharing
-                ? null : this._createObtainStreamMethod(options);
+        this.obtainStream = this._createObtainStreamMethod(options);
 
         if (!this.obtainStream) {
             logger.info('Desktop sharing disabled');