Bug 1434087, remove [moz-collapsed=true] attribute from minimal-xul.css and static atom r=bgrins

Differential Revision: https://phabricator.services.mozilla.com/D51015

--HG--
extra : moz-landing-system : lando

toolkit/content/minimal-xul.css

@@ -33,8 +33,7 @@
 }
 
 /* hide the content, but don't destroy the frames */
-[collapsed="true"],
-[moz-collapsed="true"] {
+[collapsed="true"] {
   visibility: collapse;
 }
 

xpcom/ds/StaticAtoms.py

@@ -658,7 +658,6 @@ STATIC_ATOMS = [
     Atom("mousethrough", "mousethrough"),
     Atom("mozAccessiblecaret", "moz-accessiblecaret"),
     Atom("mozCustomContentContainer", "moz-custom-content-container"),
-    Atom("mozCollapsed", "moz-collapsed"),
     Atom("mozGrabber", "mozGrabber"),
     Atom("mozNativeAnonymous", "-moz-native-anonymous"),
     Atom("mozprivatebrowsing", "mozprivatebrowsing"),