[clang-tidy] Do not trigger move fix for non-copy assignment operators in...

[clang-tidy] Do not trigger move fix for non-copy assignment operators in performance-unnecessary-value-param check

Reviewers: alexfh, sbenza, malcolm.parsons

Subscribers: JDevlieghere, cfe-commits

Differential Revision: https://reviews.llvm.org/D28899

llvm-svn: 292491