[llvm-mca] Make sure not to end the test files with an empty line.

Summary:
It's super irritating.

[properly configured] git client then complains about that double-newline,
and you have to use `--force` to ignore the warning, since even if you
fix it manually, it will be reintroduced the very next runtime :/

Reviewers: RKSimon, andreadb, courbet, craig.topper, javed.absar, gbedwell

Reviewed By: gbedwell

Subscribers: javed.absar, tschuett, gbedwell, llvm-commits

Differential Revision: https://reviews.llvm.org/D47697

llvm-svn: 333887