Port fc5c7e04

Original commit message:
There's no reason to have JavaScript wrappers for those accessors,
since the meat is already in hand-written native code (via %_DateField).
First step now to put them into native builtins. Next step will be to
completely remove %_DateField.

BUG=
TEST=test262/built-ins/Date/prototype/toISOString/15.9.5.43-0-10, test262/built-ins/Date/prototype/toISOString/15.9.5.43-0-11, test262/built-ins/Date/S15.9.3.1_A5_T1

Review URL: https://codereview.chromium.org/1569353002

Cr-Commit-Position: refs/heads/master@{#33191}