swift234

[cmake] Remove dead link directory.

This was added some time ago in case we want to build clang separate from llvm
just like we do swift. We do not actually support that though.

Currently, this just results in the main llvm binary directory being added for a
second time to the link path (i.e. this work iw asted). Thus just remove the
line but leave in a *NOTE* to deliver the message that this is where the clang
link path in such a case would need to go.