Remove use of plugInStartLabelImage
https://bugs.webkit.org/show_bug.cgi?id=108273

Reviewed by Simon Fraser.

Source/WebKit2:

Remove any use of plugInStartLabelImage. While there, implement plugInStartLabelTitle
and plugInStartLabelSubtitle to return the values from the client.
implement them.

* WebProcess/InjectedBundle/API/c/WKBundlePage.h: Remove callback and entry from client structure.
* WebProcess/InjectedBundle/InjectedBundlePageUIClient.cpp: Remove plugInStartLabelImage.
(WebKit::InjectedBundlePageUIClient::plugInStartLabelTitle): Ask the client bundle for value.
(WebKit::InjectedBundlePageUIClient::plugInStartLabelSubtitle): Ditto.

Tools:

Removed plugInStartLabelImage entry from client structure.

* WebKitTestRunner/InjectedBundle/InjectedBundlePage.cpp:
(WTR::InjectedBundlePage::InjectedBundlePage):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142347 268f45cc-cd09-0410-ab3c-d52691b4dbfc