[llvm] [Debuginfod] Remove `llvm-debuginfod-find` lit tests that used python http server.

These tests depend on `ThreadingHTTPServer` which was not introduced until python 3.7 so we might as well delete them to avoid issues. Most of their functionality is now covered by the llvm-debuginfod.test for the debuginfod server.

Reviewed By: mysterymath

Differential Revision: https://reviews.llvm.org/D119096