Rollup merge of #93290 - lcnr:same_type, r=jackh726

remove `TyS::same_type`

This function ignored regions and constants in adts, but didn't do so for references or any other types. cc https://github.com/rust-lang/rust/pull/93148#discussion_r791408057

compiler/rustc_lint/src/builtin.rs

@@ -2833,7 +2833,7 @@ impl ClashingExternDeclarations {
                 return true;
             }
             let tcx = cx.tcx;
-            if a == b || rustc_middle::ty::TyS::same_type(a, b) {
+            if a == b {
                 // All nominally-same types are structurally same, too.
                 true
             } else {