lint: promote ExtraTranslation back to being an error (#108)
lint: promote ExtraTranslation back to being an error (#108)

This doesn't seem to be needed anymore, and has the potential
to make us miss erronously removed strings - so let's bring it back.

jonalmeida/focus-android,mastizada/focus-android,Achintya999/focus-android,pocmo/focus-android,layely/focus-android,mastizada/focus-android,pocmo/focus-android,liuche/focus-android,mastizada/focus-android,ekager/focus-android,liuche/focus-android,liuche/focus-android,mozilla-mobile/focus-android,mozilla-mobile/focus-android,codebu5ter/focus-android,liuche/focus-android,Benestar/focus-android,layely/focus-android,pocmo/focus-android,ekager/focus-android,jonalmeida/focus-android,pocmo/focus-android,liuche/focus-android,layely/focus-android,liuche/focus-android,ekager/focus-android,pocmo/focus-android,jonalmeida/focus-android,codebu5ter/focus-android,layely/focus-android,ekager/focus-android,jonalmeida/focus-android,jonalmeida/focus-android,Achintya999/focus-android,ekager/focus-android,Benestar/focus-android,codebu5ter/focus-android,ekager/focus-android,Benestar/focus-android,mastizada/focus-android,Achintya999/focus-android,Benestar/focus-android,mozilla-mobile/focus-android,mozilla-mobile/focus-android,Achintya999/focus-android,mozilla-mobile/focus-android,pocmo/focus-android,Benestar/focus-android,codebu5ter/focus-android,layely/focus-android,jonalmeida/focus-android,mastizada/focus-android,mozilla-mobile/focus-android