[LinkerWrapper] Remove in-house handling of LTO

Summary:
This should be the linker's job if the user creates any bitcode files,
then passing `-flto` to the linker for the toolchain should be able to
handle it. Right now this path is only used in the case where someone
does LTO w/ ld.gold targeting a CPU so I think we are safe here as that
will still be forwarded, for bfd it'll be an error as it would on the
host. I think I talked the SYCL team out of using this as well so I
should be good to delete it.

Author: jhuber6