Remove obsolete flags from WebViewCore and WebView

Remove NO_FOCUS_CHANGE_BLOCK and BLOCK_FOCUS_CHANGE_UNTIL_KEY_UP, which were
part of SET_FINAL_FOCUS (which is no longer used) from WebViewCore.  In WebView,
do not pass BLOCK_FOCUS_CHANGE_UNTIL_KEY_UP with SET_MOVE_MOUSE, since the
receiver does not care about it.