Merge NODE_TYPE_CASTS and ELEMENT_TYPE_CASTS
https://bugs.webkit.org/show_bug.cgi?id=122735

Reviewed by Antti Koivisto.

NODE_TYPE_CASTS and ELEMENT_TYPE_CASTS are identical. Let them become one
with one another.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@157385 268f45cc-cd09-0410-ab3c-d52691b4dbfc