Remove the describe method from the QueryDescription trait

It was called directly already, but now it's even more useless since it
just forwards to the free function. Call it directly.

compiler/rustc_query_system/src/query/config.rs

@@ -49,8 +49,6 @@ impl<CTX: QueryContext, K, V> QueryVTable<CTX, K, V> {
 pub trait QueryDescription<CTX: QueryContext>: QueryConfig {
     type Cache: QueryCache<Key = Self::Key, Stored = Self::Stored, Value = Self::Value>;
 
-    fn describe(tcx: CTX, key: Self::Key) -> String;
-
     // Don't use this method to access query results, instead use the methods on TyCtxt
     fn query_state<'a>(tcx: CTX) -> &'a QueryState<Self::Key>
     where