[ASTImporter] Remove obsolete function ImportTemplateParameterList.

Summary:
The ASTNodeImporter::ImportTemplateParameterList is replaced by a
template specialization of 'import' that already exists and does
(almost) the same thing.

Reviewers: martong, a.sidorin, shafik, a_sidorin

Reviewed By: martong

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59134

llvm-svn: 356564