Revert r218616, "Refactor Matcher<T> and DynTypedMatcher to reduce overhead of casts."

MSC17, aka VS2012, cannot compile it.

  clang/include/clang/ASTMatchers/ASTMatchersInternal.h(387) : error C4519: default template arguments are only allowed on a class template

  clang/include/clang/ASTMatchers/ASTMatchersInternal.h(443) : see reference to class template instantiation 'clang::ast_matchers::internal::Matcher<T>' being compiled