Delete the removeCallEdgeTo callgraph method,

because it does not maintain a correct list
of callsites.  I discovered (see following
commit) that the inliner will create a wrong
callgraph if it is fed a callgraph with
correct edges but incorrect callsites.  These
were created by Prune-EH, and while it wasn't
done via removeCallEdgeTo, it could have been
done via removeCallEdgeTo, which is an accident
waiting to happen.  Use removeCallEdgeFor
instead.

llvm-svn: 55859