clang CoverageMapping tests bot cleanup

Summary:
D82928 generated unexpected tmp files in the CoverageMapping test directory. This patch cleans it up and remove the file in the test bots.
It will be revered after a week.

Reviewers: thakis

Reviewed By: thakis

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D82992