Remove NeedsFocusAppearanceUpdateSoonAfterAttach flag

This was used a hack to allow an element that wasn't really focusable to
become the focused element while the stylesheets were loading and then
decide if it should really be focused later. Presumably this means you
could focus an element that used -webkit-user-modify in the CSS before
that CSS was loaded and then we would focus it when the CSS loaded.

The code didn't work though because it just deferred until attach, but
after the call to updateLayoutIgnorePendingStylesheets() which would have
attached the focused element. So it could only work if you forced a
reattach.

Since it didn't really work, and it's not clear how pages could depend on
this racy behavior lets just remove it.

Note: I once tried to make this hack work properly in
https://codereview.chromium.org/176813007/ but it turned out it's more
effort than it's worth and other browsers don't have this behavior anyway.

R=eseidel@chromium.org, ojan@chromium.org

Review URL: https://codereview.chromium.org/267723013

git-svn-id: svn://svn.chromium.org/blink/trunk@173250 bbb929c8-8fbe-4397-9dbb-9b2b20218538