Rollup merge of rust-lang#119107 - lcnr:uwuwu, r=compiler-errors

subtype_predicate: remove unnecessary probe

There is no reason to probe here. The failure either results in an actual type error, in which cases the probe is useless, or it is used inside of evaluate, in which case we're already inside of the `fn evaluation_probe`, so it is also not necessary.

compiler/rustc_infer/src/infer/mod.rs

@@ -713,10 +713,6 @@ impl<'tcx> InferCtxtBuilder<'tcx> {
 }
 
 impl<'tcx, T> InferOk<'tcx, T> {
-    pub fn unit(self) -> InferOk<'tcx, ()> {
-        InferOk { value: (), obligations: self.obligations }
-    }
-
     /// Extracts `value`, registering any obligations into `fulfill_cx`.
     pub fn into_value_registering_obligations(
         self,
@@ -1025,15 +1021,10 @@ impl<'tcx> InferCtxt<'tcx> {
             _ => {}
         }
 
-        Ok(self.commit_if_ok(|_snapshot| {
-            let ty::SubtypePredicate { a_is_expected, a, b } =
-                self.instantiate_binder_with_placeholders(predicate);
-
-            let ok =
-                self.at(cause, param_env).sub_exp(DefineOpaqueTypes::No, a_is_expected, a, b)?;
+        let ty::SubtypePredicate { a_is_expected, a, b } =
+            self.instantiate_binder_with_placeholders(predicate);
 
-            Ok(ok.unit())
-        }))
+        Ok(self.at(cause, param_env).sub_exp(DefineOpaqueTypes::No, a_is_expected, a, b))
     }
 
     pub fn region_outlives_predicate(