factor out the rvalue lifetime rule

remove region_scope_tree from RegionCtxt

Apply suggestions from code review

Co-authored-by: Niko Matsakis <niko@alum.mit.edu>

compiler/rustc_middle/src/query/mod.rs

@@ -1048,12 +1048,6 @@ rustc_queries! {
         desc { "reachability" }
     }
 
-    /// Per-body `region::ScopeTree`. The `DefId` should be the owner `DefId` for the body;
-    /// in the case of closures, this will be redirected to the enclosing function.
-    query region_scope_tree(def_id: DefId) -> &'tcx region::ScopeTree {
-        desc { |tcx| "computing drop scopes for `{}`", tcx.def_path_str(def_id) }
-    }
-
     /// Generates a MIR body for the shim.
     query mir_shims(key: ty::InstanceDef<'tcx>) -> mir::Body<'tcx> {
         storage(ArenaCacheSelector<'tcx>)