compiler: Don't mark SingleUseConsts MIR pass as "required for soundness"

Because:
* Something like it did not exist before PR 107404
* That it is not run our mir-opt-level 0 indicates that it is not required for soundness
* No test fails in PR 151426 that stops enabling by default in non-optimized builds

Author: Enselic

compiler/rustc_mir_transform/src/single_use_consts.rs

@@ -85,7 +85,7 @@ impl<'tcx> crate::MirPass<'tcx> for SingleUseConsts {
     }
 
     fn is_required(&self) -> bool {
-        true
+        false
     }
 }