Revert "[clang] Fix absolute file paths with -fdebug-prefix-map"

This reverts commit a23a5967.

This broke a windows test https://buildkite.com/llvm-project/premerge-checks/builds/59492#7dad207c-6cbe-40ad-95e4-c48b47fe2527

Differential Revision: https://reviews.llvm.org/D111444