[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

GitOrigin-RevId: a3b099b68c0c156aa8ed9ec81c5dfdf150c6329c
diff --git a/docs/UsersManual.rst b/docs/UsersManual.rst
index f534b21..ce66ef5 100644
--- a/docs/UsersManual.rst
+++ b/docs/UsersManual.rst
@@ -3716,7 +3716,6 @@
       /Zc:trigraphs           Enable trigraphs
       /Zc:twoPhase-           Disable two-phase name lookup in templates
       /Zc:twoPhase            Enable two-phase name lookup in templates
-      /Zd                     Emit debug line number tables only
       /Zi                     Alias for /Z7. Does not produce PDBs.
       /Zl                     Don't mention any default libraries in the object file
       /Zp                     Set the default maximum struct packing alignment to 1