[llvm-driver] Temporarily remove dsymutil

A recent change made it such that target_link_libraries is always
called and not conditionally. target_link_libraries doesn't
currently work when LLVM_TOOL_LLVM_DRIVER_BUILD=On. This should
be fixed in the future, but for now let's just remove dsymutil
as part of the llvm-driver build.

Differential Revision: https://reviews.llvm.org/D139588