[Glitch] Upgrade to react-router v5

Port 1b70d7ed7c to glitch-soc

Co-authored-by: Claire <claire.github-309c@sitedethib.com>
Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/features/getting_started_misc/index.jsx

@@ -28,7 +28,6 @@ const messages = defineMessages({
 class GettingStartedMisc extends ImmutablePureComponent {
 
   static contextTypes = {
-    router: PropTypes.object.isRequired,
     identity: PropTypes.object,
   };