Workaround fix for bug #117141 (Composer crashes when loading pages with an HTML Select element [@FrameManager::GetPrimaryFrameFor])

Removed seemingly unnecessary selection UI Style rule for -moz-dropdown-list,
to workaround the crash that happens during the restyling of the HTML Select
element when the EditorOverride.css style sheet is loaded.

r=brade@netscape.com  sr=sfraser@netscape.com

editor/composer/src/res/EditorOverride.css

@@ -86,10 +86,6 @@ label {
   -moz-user-select: text !important;
 }
 
-:-moz-dropdown-list {
-  -moz-user-select: text !important;
-} 
-
 option {
   -moz-user-select: text !important;
 }

editor/ui/composer/content/EditorOverride.css

@@ -86,10 +86,6 @@ label {
   -moz-user-select: text !important;
 }
 
-:-moz-dropdown-list {
-  -moz-user-select: text !important;
-} 
-
 option {
   -moz-user-select: text !important;
 }