[PM] Remove an unused and rather expensive mapping from an analysis
group's interface to all of the implementations of that analysis group.
The groups themselves can and do manage this anyways, the pass registry
needn't involve itself.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219097 91177308-0d34-0410-b5e6-96231b3b80d8