Remove Drop-caused migration-added captures

All of these were added due to insignificant Drop types being present.

clippy_utils/src/lib.rs

@@ -990,10 +990,7 @@ fn visit_pat(&mut self, p: &'tcx Pat<'tcx>) {
         captures: HirIdMap::default(),
     };
     v.visit_expr(expr);
-    v.allow_closure.then(|| {
-        let _ = &v;
-        v.captures
-    })
+    v.allow_closure.then(|| v.captures)
 }
 
 /// Returns the method names and argument list of nested method call expressions that make up