clippy::complexity fixes

filter_next
needless_question_mark
bind_instead_of_map
manual_find
derivable_impls
map_identity
redundant_slicing
skip_while_next
unnecessary_unwrap
needless_bool

compiler/rustc_transmute/src/maybe_transmutable/query_context.rs

@@ -76,11 +76,7 @@ mod rustc {
                 }
             };
 
-            let ret = if self.visibility(def_id).is_accessible_from(parent, *self) {
-                true
-            } else {
-                false
-            };
+            let ret: bool = self.visibility(def_id).is_accessible_from(parent, *self);
 
             trace!(?ret, "ret");
             ret