Merge branch 'remove-signin-flash' into 'master'

Remove success signin message by devise

I find it really annoying every time I login into GitLab it shows me
that I successfully signed in. But this makes no sense to me. I already
see dashboard and dont see login screen. Its obvious I signed in
successfully. Instead it just show annyoing message every time taking
part of space on my screen.

See merge request !401

config/locales/devise.en.yml

@@ -23,8 +23,8 @@ en:
       timeout: 'Your session expired, please sign in again to continue.'
       inactive: 'Your account was not activated yet.'
     sessions:
-      signed_in: 'Signed in successfully.'
-      signed_out: 'Signed out successfully.'
+      signed_in: ''
+      signed_out: ''
     users_sessions:
       user:
         signed_in: 'Signed in successfully.'