Don't use anon for query erase_and_anonymize_regions_ty

According to its comment, this query was only using `anon` to save a little bit
of work for a dep graph node that is expected to have no dependencies.

Benchmarks indicate that the perf loss, if any, is small enough to be justified
by the fact that we can now remove support for `anon` queries.

Adding `no_hash` appears to give marginally better perf results.

Author: Zalathar

compiler/rustc_middle/src/queries.rs

@@ -767,14 +767,10 @@ rustc_queries! {
     /// Normally you would just use `tcx.erase_and_anonymize_regions(value)`,
     /// however, which uses this query as a kind of cache.
     query erase_and_anonymize_regions_ty(ty: Ty<'tcx>) -> Ty<'tcx> {
-        // This query is not expected to have input -- as a result, it
-        // is not a good candidates for "replay" because it is essentially a
-        // pure function of its input (and hence the expectation is that
-        // no caller would be green **apart** from just these
-        // queries). Making it anonymous avoids hashing the result, which
-        // may save a bit of time.
-        anon
         desc { "erasing regions from `{}`", ty }
+        // Not hashing the return value appears to give marginally better perf for this query,
+        // which should always be marked green for having no dependencies anyway.
+        no_hash
     }
 
     query wasm_import_module_map(_: CrateNum) -> &'tcx DefIdMap<String> {