Revert "Support object spread in walk"
Revert "Support object spread in walk"

This reverts commit 7d3267d161f9af3b5c6d44c5ffe878f1f3dd79c9.

It caused names in object patterns to be walked as expressions, rather
than patterns, breaking `blint` and possibly other uses.

ternjs/acorn,marijnh/acorn,TimothyGu/acorn,marijnh/acorn,mysticatea/acorn,TimothyGu/acorn,mysticatea/acorn,mysticatea/acorn,TimothyGu/acorn,ternjs/acorn,ternjs/acorn,marijnh/acorn