Remove YAML/Native round-trip passes.

The round-trip passes were introduced in r193300. The intention of
the change was to make sure that LLD is capable of reading end
writing such file formats.

But that turned out to be yet another over-designed stuff that had
been slowing down everyday development.

The passes ran after the core linker and before the writer. If you
had an additional piece of information that needs to be passed from
front-end to the writer, you had to invent a way to save the data to
YAML/Native. These passes forced us to do that even if that data
was not needed to be represented neither in an object file nor in
an executable/DSO. It doesn't make sense. We don't need these passes.

http://reviews.llvm.org/D7480

llvm-svn: 230069