allow screenOrientation for ChatActivity

this was temporarily disabled as a workaround because of https://github.com/nextcloud/talk-android/issues/3146
So after screen rotation it could happen that chat was not updated.

Now that the issue is solved, portrait mode will be allowed again

Signed-off-by: Marcel Hibbe <dev@mhibbe.de>

app/src/main/AndroidManifest.xml

@@ -215,7 +215,6 @@
 
         <activity
             android:name=".chat.ChatActivity"
-            android:screenOrientation="portrait"
             android:theme="@style/AppTheme" />
 
         <activity