[Docs] Removed /Zd flag still mentioned in documentation

https://reviews.llvm.org/D93458 removed the /Zd flag as MSVC doesn't support that syntax. Instead users should be using -gline-tables-only.
The /Zd flag is still mentioned at https://clang.llvm.org/docs/UsersManual.html#clang-cl :   /Zd                     Emit debug line number tables only.

Fix PR52571

Reviewed By: xgupta

Differential Revision: https://reviews.llvm.org/D114632