[gn build] Don't pass -fuse-ld=lld to compiler-rt tests

This was done for check-hwasan, but compiler-rt/test/hwasan/lit.cfg.py
already does that.

This makes check-asan (to be submitted) fail on Windows due to using
lld-link (as opposed to MSVC link.exe) in tests. That seems like a
problem that should be fixed, but that's orthogonal to this patch.