Previously, the Intl implementation tracked types two ways:
 - In the intl_initialized_marker_symbol
 - In various named properties of the intl_impl_object_symbol value

As far as I can tell, these will never disagree with each other,
modulo bugs in Intl itself. This patch removes the second type
checking system.

BUG=v8:5751

Review-Url: https://codereview.chromium.org/2591203002
Cr-Commit-Position: refs/heads/master@{#41941}