[debuginfo] Remove obsolete test_debuginfo.pl that was moved to debuginfo-tests.

Summary:
Now that r320495, "[debuginfo-tests] Support moving
debuginfo-tests to llvm/projects," has landed, which includes a local
copy of test_debuginfo.pl, remove the obsolete copy.

Reviewers: zturner, aprantl

Reviewed By: aprantl

Subscribers: llvm-commits, JDevlieghere

Differential Revision: https://reviews.llvm.org/D41260

llvm-svn: 320771