Remove unused non-terminal

The non-terminal `patterns` is not used any more. This CL removes the
rule where it is introduced.

Change-Id: I2a8e957957d71999807a0e00fe102e61ed5ec173
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/288202
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Erik Ernst <eernst@google.com>

tools/spec_parser/Dart.g

@@ -3,6 +3,8 @@
 // BSD-style license that can be found in the LICENSE file.
 
 // CHANGES:
+// v0.32 Remove unused non-terminal `patterns`.
+//
 // v0.31 Inline `identifierNotFUNCTION` into `identifier`. Replace all
 // other references with `identifier` to match the spec.
 //
@@ -1038,10 +1040,6 @@ pattern
     :    logicalOrPattern
     ;
 
-patterns
-    :    pattern (',' pattern)* ','?
-    ;
-
 logicalOrPattern
     :    logicalAndPattern ('||' logicalAndPattern)*
     ;