Remove llvm-ld and llvm-stub (which is only used by llvm-ld).

llvm-ld is no longer useful and causes confusion and so it is being removed.

* Does not work very well on Windows because it must call a gcc like driver to
  assemble and link.
* Has lots of hard coded paths which are wrong on many systems.
* Does not understand most of ld's options.
* Can be partially replaced by llvm-link | opt | {llc | as, llc -filetype=obj} |
  ld, or fully replaced by Clang.

I know of no production use of llvm-ld, and hacking use should be
replaced by Clang's driver.

llvm-svn: 155147