fix(audio-share): Show button only when supported by browser.

Show the audio share button only when its supported. For example, mobile browsers do not support getDisplayMedia yet.

react/features/toolbox/components/web/Toolbox.js

      */
     _renderOverflowMenuContent(additionalButtons: Array<React$Element<any>>) {
         const {
+            _desktopSharingEnabled,
             _feedbackConfigured,
             _fullScreen,
             _isMobile,
                 && <SharedVideoButton
                     key = 'sharedvideo'
                     showLabel = { true } />,
-            this._shouldShowButton('shareaudio') && isScreenAudioSupported()
+            this._shouldShowButton('shareaudio')
+                && _desktopSharingEnabled
+                && isScreenAudioSupported()
                 && <OverflowMenuItem
                     accessibilityLabel = { t('toolbar.accessibilityLabel.shareaudio') }
                     icon = { IconShareAudio }