[CPP,GObject,ObjC] Add 'enum' skip to CodeGenerator{CPP,GObject,ObjC}.pm
https://bugs.webkit.org/show_bug.cgi?id=108565

Patch by Nils Barth <nbarth@google.com> on 2013-01-31
Reviewed by Kentaro Hara.

Since legacy code generators (CodeGenerator{CPP,GObject,ObjC}.pm)
do not support enumerations, add test to skip attributes of enum type.
This lets us remove #if macro from enum in test file and not need
these in future.
Also minor associated code cleaning:
  auxiliary variable: $type = $attribute->signature->type.

Test: bindings/scripts/test/TestObj.idl (run-bindings-test)

* bindings/scripts/CodeGeneratorCPP.pm:
(SkipAttribute):
* bindings/scripts/CodeGeneratorGObject.pm:
(SkipAttribute):
* bindings/scripts/CodeGeneratorObjC.pm:
(SkipAttribute):
* bindings/scripts/test/TestObj.idl: remove #if macro

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141541 268f45cc-cd09-0410-ab3c-d52691b4dbfc