IDL compiler: sync Python to r167001

Python side to:
Remove isolated world parameters from event listener attributes
https://codereview.chromium.org/149803005/

Nice cleanup!

BUG=239771
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/162583002

git-svn-id: svn://svn.chromium.org/blink/trunk@167063 bbb929c8-8fbe-4397-9dbb-9b2b20218538