dawn_wire: Remove unused support of "const*const*"

This patch removes the support of annotation "const*const*" in
the template WireCmd.cpp as it is not used in current Dawn wire
implementation.

BUG=chromium:1266727

Change-Id: I4c4d68ccc050edb5f855094910440e90aef2bc4a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/72040
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>

generator/dawn_json_generator.py

@@ -594,8 +594,6 @@ def decorate(name, typ, arg):
         return typ + ' * ' + name
     elif arg.annotation == 'const*':
         return typ + ' const * ' + name
-    elif arg.annotation == 'const*const*':
-        return 'const ' + typ + '* const * ' + name
     else:
         assert False