[clang-tidy] performance-unnecessary-copy-initialization: Remove the complete...

[clang-tidy] performance-unnecessary-copy-initialization: Remove the complete statement when the copied variable is unused.

It is not useful to keep the statement around and can lead to compiler
warnings when -Wall (-Wunused-variable specifically) turned on.

Differential Revision: https://reviews.llvm.org/D102175

Reviewed-by: ymandel