Make the "attach_inlines" parameter to "differential.createcomment" a no-op

Summary: Ref T13513. See that task for some discussion. This prepares to lift "loadUnsubmittedInlineComments(...)" into shared code.

Test Plan: Grepped for callers, found none in the upstream. This is a backward compatibilty break. See T13513.

Maniphest Tasks: T13513

Differential Revision: https://secure.phabricator.com/D21225