[Dominators] Simplify templates

Summary: DominatorTreeBase and related classes used overcomplicated template machinery. This patch simplifies them and gets rid of DominatorTreeBaseTraits and DominatorTreeBaseByTraits, which weren't actually used outside the DomTree construction.

Reviewers: dberlin, sanjoy, davide, grosser

Reviewed By: dberlin, davide, grosser

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35285

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307953 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed