[cleanup] Fix up trailing whitespace and formatting in the pass regitsry
code prior to hacking on it more significantly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219094 91177308-0d34-0410-b5e6-96231b3b80d8
[cleanup] Switch to using range-based for loops in two very obvious
places.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219095 91177308-0d34-0410-b5e6-96231b3b80d8
[PM] Remove the (deeply misguided) 'unregister' functionality from the
pass registry.

This style of registry is somewhat questionable, but it being
non-monotonic is crazy. No one is (or should be) unloading DSOs with
passes and unregistering them here. I've checked with a few folks and
I don't know of anyone using this functionality or any important use
case where it is necessary.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219096 91177308-0d34-0410-b5e6-96231b3b80d8
[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