Remove AssignmentPattern.operator when explicitly parsing binding.
Remove AssignmentPattern.operator when explicitly parsing binding.

Closes #301.

btmills/acorn,TimothyGu/acorn,Rich-Harris/acorn,happibum/acorn,marijnh/acorn,marijnh/acorn,ternjs/acorn,btmills/acorn,mysticatea/acorn,mysticatea/acorn,TimothyGu/acorn,ajaxorg/acorn,mathiasbynens/acorn,mathiasbynens/acorn,happibum/acorn,mathiasbynens/acorn,ternjs/acorn,ternjs/acorn,Rich-Harris/acorn,ajaxorg/acorn,TimothyGu/acorn,btmills/acorn,mysticatea/acorn,MarcelGerber/acorn,ajaxorg/acorn,Rich-Harris/acorn,happibum/acorn,MarcelGerber/acorn,marijnh/acorn,MarcelGerber/acorn