remove unused pred_rcache

compiler/rustc_middle/src/ty/context.rs

@@ -1370,7 +1370,6 @@ pub struct GlobalCtxt<'tcx> {
 
     // Internal caches for metadata decoding. No need to track deps on this.
     pub ty_rcache: Lock<FxHashMap<ty::CReaderCacheKey, Ty<'tcx>>>,
-    pub pred_rcache: Lock<FxHashMap<ty::CReaderCacheKey, Predicate<'tcx>>>,
 
     /// Caches the results of trait selection. This cache is used
     /// for things that do not have to do with the parameters in scope.
@@ -1601,7 +1600,6 @@ pub fn create_global_ctxt<T>(
             query_system,
             query_kinds,
             ty_rcache: Default::default(),
-            pred_rcache: Default::default(),
             selection_cache: Default::default(),
             evaluation_cache: Default::default(),
             new_solver_evaluation_cache: Default::default(),