Bug 1772513 - Don't require unified build in widget/gtk. r=stransky

This also ensures on automation that we don't regress this.

Depends on D148256

Differential Revision: https://phabricator.services.mozilla.com/D148257

widget/gtk/moz.build

@@ -187,6 +187,5 @@ if CONFIG["MOZ_ENABLE_DBUS"]:
         "AsyncDBus.cpp",
     ]
     CXXFLAGS += CONFIG["MOZ_DBUS_GLIB_CFLAGS"]
-CXXFLAGS += ["-Werror=switch"]
 
-REQUIRES_UNIFIED_BUILD = True
+CXXFLAGS += ["-Werror=switch"]