Get rid of WTF::IsSubclassOfTemplate<N> classes

The WTF::IsSubclassOfTemplate<N> classes can be removed if
the WTF::IsSubclassOfTemplate class uses variadic templates.

Review URL: https://codereview.chromium.org/616123003

git-svn-id: svn://svn.chromium.org/blink/trunk@183105 bbb929c8-8fbe-4397-9dbb-9b2b20218538