Move EarlyOtherwiseBranch to mir-opt-level 2

This didn't have an effect in most cases, and is not trivially sound.
Let it bake at `mir-opt-level=2` for a while.

Author: ecstatic-morse

compiler/rustc_mir/src/transform/early_otherwise_branch.rs

@@ -29,7 +29,7 @@ pub struct EarlyOtherwiseBranch;
 
 impl<'tcx> MirPass<'tcx> for EarlyOtherwiseBranch {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, source: MirSource<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.opts.debugging_opts.mir_opt_level < 1 {
+        if tcx.sess.opts.debugging_opts.mir_opt_level < 2 {
             return;
         }
         trace!("running EarlyOtherwiseBranch on {:?}", source);