Remove a whole bunch of horrible hacky code that was used to promote allocas

Remove a whole bunch of horrible hacky code that was used to promote allocas
whose addresses where used by trivial phi nodes and select instructions.  This
is now performed by the instcombine pass, which is more powerful, is much
simpler, and is faster.  This allows the deletion of a bunch of code, two
FIXME's and two gotos.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16406 91177308-0d34-0410-b5e6-96231b3b80d8