parser: Do not call bump recursively

Token normalization is merged directly into `bump`.
Special "unknown macro variable" diagnostic for unexpected `$`s is removed as preventing legal code from compiling.

src/test/ui/issues/issue-6596-1.rs

@@ -1,7 +1,7 @@
 macro_rules! e {
     ($inp:ident) => (
         $nonexistent
-        //~^ ERROR unknown macro variable `nonexistent`
+        //~^ ERROR expected expression, found `$`
     );
 }
 

src/test/ui/issues/issue-6596-1.stderr

@@ -1,8 +1,8 @@
-error: unknown macro variable `nonexistent`
+error: expected expression, found `$`
   --> $DIR/issue-6596-1.rs:3:9
    |
 LL |         $nonexistent
-   |         ^^^^^^^^^^^^ unknown macro variable
+   |         ^^^^^^^^^^^^ expected expression
 ...
 LL |     e!(foo);
    |     -------- in this macro invocation

src/test/ui/issues/issue-6596-2.rs

@@ -3,7 +3,7 @@
 macro_rules! g {
     ($inp:ident) => (
         { $inp $nonexistent }
-        //~^ ERROR unknown macro variable `nonexistent`
+        //~^ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `$`
     );
 }
 

src/test/ui/issues/issue-6596-2.stderr

@@ -1,8 +1,8 @@
-error: unknown macro variable `nonexistent`
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `$`
   --> $DIR/issue-6596-2.rs:5:16
    |
 LL |         { $inp $nonexistent }
-   |                ^^^^^^^^^^^^ unknown macro variable
+   |                ^^^^^^^^^^^^ expected one of 8 possible tokens
 ...
 LL |     g!(foo);
    |     -------- in this macro invocation