Remove obsolete Temasys workaround on React Native

jitsi/lib-jitsi-meet#66b601e disabled the execution of Temasys'
adapter.screenshare.js on browsers on which we don't use Temasys such as
React Native. Henceforth, no Temasys workarounds are necessary on React
Native.

react/features/base/lib-jitsi-meet/native/polyfills-browser.js

                 }
             }
 
-            // Required by:
-            // - lib-jitsi-meet/modules/RTC/adapter.screenshare.js
-            userAgent += ' Chrome/31.';
-
             navigator.userAgent = userAgent;
         })();
     }