clang-cl: Remove /Zd flag

cl.exe doesn't understand Zd (in either MSVC 2017 or 2019), so neiter
should we. It used to do the same as `-gline-tables-only` which is
exposed as clang-cl flag as well, so if you want this behavior, use
`gline-tables-only`. That makes it clear that it's a clang-cl-only flag
that won't work with cl.exe.

Motivated by the discussion in D92958.

Differential Revision: https://reviews.llvm.org/D93458