After 1564083002, spread expressions are desugared and should not
survive in the AST after parsing. This patch removes dead code
related to this.  It also eliminates the kSpread bailout reason
and the concat_iterable_to_array_builtin.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1592713002

Cr-Commit-Position: refs/heads/master@{#33385}