[PM/AA] Stop getting the TargetLibraryInfo out of the AliasAnalysis and

[PM/AA] Stop getting the TargetLibraryInfo out of the AliasAnalysis and
just depend on it directly.

This was particularly frustrating because there was a really wide
mixture of using a member variable and re-extracting it from the AA that
happened to be around. I think the result is much more clear.

I've also deleted all of the pointless null checks and used references
across the APIs where I could to make it explicit that this cannot be
null in a useful fashion.

llvm-svn: 244780