List platforms that still use the legacy clipboard instead of just saying "not Mac"
https://bugs.webkit.org/show_bug.cgi?id=116177

Reviewed by Andreas Kling.

* dom/Clipboard.h: Replaced the "!MAC || IOS" with a list of platforms still on the
legacy model.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150152 268f45cc-cd09-0410-ab3c-d52691b4dbfc