IDL parser: drop AttributeOrOperation and StaticAttribute overrides

Static attributes are now supported by the base IDL parser, so these
overrides are no longer needed.

Followup to:
IDL parser: add StaticAttribute production
https://codereview.chromium.org/333853002/

...and prep for:
IDL parser: align with current Web IDL specification
https://codereview.chromium.org/329853005/

Review URL: https://codereview.chromium.org/336733002

git-svn-id: svn://svn.chromium.org/blink/trunk@176398 bbb929c8-8fbe-4397-9dbb-9b2b20218538