Service Workers: Remove overloads for optional Dictionary arguments

Trailing optional Dictionary are automagically handled by bindings,
with a new empty dictionary passed in if the argument is not
specified by script. Overloads are not needed in this case.

BUG=373120

Review URL: https://codereview.chromium.org/717283002

git-svn-id: svn://svn.chromium.org/blink/trunk@185312 bbb929c8-8fbe-4397-9dbb-9b2b20218538