don't break parser error recovery in presence of macros

Parser has the invariant that `{}` are balanced.
Previous code tried (unsucesfuly) maintain the same invariant for
`$()` as well, but it was done in a rather ad-hoc manner: it's not at
all obvious that it is possible to maintain both invariants!

crates/ra_parser/src/parser.rs

@@ -5,7 +5,7 @@ use drop_bomb::DropBomb;
 use crate::{
     event::Event,
     ParseError,
-    SyntaxKind::{self, EOF, ERROR, L_DOLLAR, R_DOLLAR, TOMBSTONE},
+    SyntaxKind::{self, EOF, ERROR, TOMBSTONE},
     TokenSet, TokenSource, T,
 };
 
@@ -212,7 +212,7 @@ impl<'t> Parser<'t> {
     /// Create an error node and consume the next token.
     pub(crate) fn err_recover(&mut self, message: &str, recovery: TokenSet) {
         match self.current() {
-            T!['{'] | T!['}'] | L_DOLLAR | R_DOLLAR => {
+            T!['{'] | T!['}'] => {
                 self.error(message);
                 return;
             }