Removed fileCard GA labs flag

refs https://github.com/TryGhost/Team/issues/1258

- labs flag conditionals have been removed from Admin so the GA flag is no longer necessary

core/shared/labs.js

@@ -15,7 +15,6 @@ const messages = {
 
 // flags in this list always return `true`, allows quick global enable prior to full flag removal
 const GA_FEATURES = [
-    'fileCard',
     'headerCard'
 ];