CodeGen: Remove implicit conversions from Analysis and BranchFolding

Remove a few more implicit ilist iterator conversions, this time from
Analysis.cpp and BranchFolding.cpp.

I added a few overloads for `remove()` and `erase()`, which quite
naturally take pointers as well as iterators as parameters.  This will
reduce the churn at least in the short term, but I don't really have a
problem with these existing for longer.

llvm-svn: 249867