[llvm-cov] Temporary delete sources-specified.test, it is failing on some bots.

Summary: http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/5950/steps/test-stage1-compiler/logs/stdio

Reviewers: vsk, Dor1s

Reviewed By: Dor1s

Subscribers: mehdi_amini

Differential Revision: https://reviews.llvm.org/D38888

llvm-svn: 315693