[clang-tidy] Do not issue fixit for explicit template specializations

Summary:

Do not issue fixit in UnnecessaryValueParamCheck if the function is an explicit template specialization as this could cause build breakages.

Reviewers: alexfh

Subscribers: JDevlieghere, xazax.hun, cfe-commits

Differential Revision: https://reviews.llvm.org/D35718

llvm-svn: 309067