ghc & docs: kill unused flags

This removes the following, now defunct flags, which will not be
recognized by GHC 7.10:

  -fwarn-lazy-unlifted-bindings
  -pgmm and -optm (used for the Mangler, long dead)
  -keep-raw-s-file & -keep-raw-s-files
  -monly[432]-reg-only

Signed-off-by: Austin Seipp <austin@well-typed.com>