[XLA:LLVM] Remove SetTbaaForInstruction.

This was made a nop some time ago because it was broken; this patch
removes it entirely.

I don't think we can sensibly use HLO types for alias analysis -- a
buffer may store values of different HLO types over its lifetime.  This
isn't an indictment against LLVM TBAA in general; we may be able to use
it for something other than AA based on HLO types.

PiperOrigin-RevId: 171330686