Remove didCompleteRubberBandForMainFrame UIClient callback

Remove didCompleteRubberBandForMainFrame UIClient callback
https://bugs.webkit.org/show_bug.cgi?id=69161

Reviewed by Adam Roben.

* UIProcess/API/C/WKPage.h:
* UIProcess/WebPageProxy.cpp:
* UIProcess/WebPageProxy.h:
* UIProcess/WebPageProxy.messages.in:
* UIProcess/WebUIClient.cpp:
* UIProcess/WebUIClient.h:
* WebProcess/WebCoreSupport/WebChromeClient.cpp:
(WebKit::WebChromeClient::didCompleteRubberBandForFrame):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96413 268f45cc-cd09-0410-ab3c-d52691b4dbfc