[Mac] Remove the ClipboardMac class and header file
https://bugs.webkit.org/show_bug.cgi?id=116165

Reviewed by Anders Carlsson.

Source/WebCore:

* WebCore.xcodeproj/project.pbxproj: Remove ClipboardMac.h.
* editing/mac/EditorMac.mm: Import Clipboard.h rather than ClipboardMac.h.
* page/mac/EventHandlerMac.mm: Ditto.
* platform/mac/ClipboardMac.h: Removed.

* platform/mac/ClipboardMac.mm: Import Clipboard.h rather than ClipboardMac.h.
Deleted ClipboardMac constructor.

Source/WebKit/mac:

* WebCoreSupport/WebDragClient.mm: Import Clipboard.h instead of ClipboardMac.h.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150129 268f45cc-cd09-0410-ab3c-d52691b4dbfc