Revert "Stabilize $$ in Rust 1.63.0"

This reverts commit 9edaa76adc.

compiler/rustc_expand/src/mbe/quoted.rs

@@ -234,6 +234,8 @@ fn parse_tree(
                             sess,
                             &Token { kind: token::Dollar, span },
                         );
+                    } else {
+                        maybe_emit_macro_metavar_expr_feature(features, sess, span);
                     }
                     TokenTree::token(token::Dollar, span)
                 }