[gn build] Remove unnecessary lld dependency on DebugInfo/Symbolize.

The gn script for lld's COFF lib adds an unnecessary dependency on llvm/lib/DebugInfo/Symbolize. There is no such dependency in lld/COFF/CMakeLists.txt. This can be safely removed.

Reviewed By: phosek, thakis

Differential Revision: https://reviews.llvm.org/D115554