[clang-tidy] Fix a false positive about C++17 deduced class template types in...

[clang-tidy] Fix a false positive about C++17 deduced class template types in unused-using-decl check.

Reviewers: gribozavr2

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D73876