Consolidate obligation cause codes for where clauses

compiler/rustc_borrowck/src/region_infer/mod.rs

@@ -2059,10 +2059,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
                     // We currently do not store the `DefId` in the `ConstraintCategory`
                     // for performances reasons. The error reporting code used by NLL only
                     // uses the span, so this doesn't cause any problems at the moment.
-                    Some(ObligationCauseCode::SpannedWhereClause(
-                        CRATE_DEF_ID.to_def_id(),
-                        predicate_span,
-                    ))
+                    Some(ObligationCauseCode::WhereClause(CRATE_DEF_ID.to_def_id(), predicate_span))
                 } else {
                     None
                 }