rustc_ast_pretty: Don't print space after $

For example, this code:

    $arg:expr

used to be pretty-printed as:

    $ arg : expr

but is now pretty-printed as:

    $arg : expr

src/test/ui/hygiene/unpretty-debug.stdout

@@ -8,7 +8,7 @@
 #![feature /* 0#0 */(no_core)]
 #![no_core /* 0#0 */]
 
-macro_rules! foo /* 0#0 */ { ($ x : ident) => { y + $ x } }
+macro_rules! foo /* 0#0 */ { ($x : ident) => { y + $x } }
 
 fn bar /* 0#0 */() {
     let x /* 0#0 */ = 1;

src/test/ui/proc-macro/meta-macro-hygiene.stdout

@@ -30,7 +30,7 @@ macro_rules! produce_it
     */ {
     () =>
     {
-        meta_macro :: print_def_site! ($ crate :: dummy! ()) ;
+        meta_macro :: print_def_site! ($crate :: dummy! ()) ;
         // `print_def_site!` will respan the `$crate` identifier
         // with `Span::def_site()`. This should cause it to resolve
         // relative to `meta_macro`, *not* `make_macro` (despite

src/test/ui/proc-macro/nonterminal-token-hygiene.stdout

@@ -50,9 +50,9 @@ macro_rules! outer
     /*
     0#0
     */ {
-    ($ item : item) =>
+    ($item : item) =>
     {
-        macro inner() { print_bang! { $ item } } inner! () ;
+        macro inner() { print_bang! { $item } } inner! () ;
 
     } ;
 }