iOS does not use CaptionUserPreferencesMac
https://bugs.webkit.org/show_bug.cgi?id=110259

Reviewed by Dean Jackson.

* page/CaptionUserPreferencesMac.h: Add PLATFORM(IOS) guard
* page/CaptionUserPreferencesMac.mm: Ditto.

* page/PageGroup.cpp:
(WebCore::PageGroup::captionPreferences): Ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143469 268f45cc-cd09-0410-ab3c-d52691b4dbfc