Notice for out-of-tree maintainer: RegisterScheduler::setDefault removed

Hi all,

Just a notice for out-of-tree maintainer, I removed RegisterScheduler::setDefault in r243388. It was used to override the default command line option that selects the DAG scheduler to use.

Instead of hacking into the command line plumbing, a target that wants more control over the selection of the scheduler than it already has with setSchedulingPreference has a SubTargetHook “getDAGScheduler” that can be overridden. The original motivation for this change was to remove some mutable global state.

(Now with the contemporary llvm-dev list; sorry for the noise.)