Remove ChromeClient::scrollbarsModeDidChange

Remove ChromeClient::scrollbarsModeDidChange
https://bugs.webkit.org/show_bug.cgi?id=175805

Patch by Alex Christensen <achristensen@webkit.org> on 2017-08-22
Reviewed by Daniel Bates.

Source/WebCore:

No change in behavior.  It was never called, and no implementations did anything.

* loader/EmptyClients.h:
* page/Chrome.cpp:
(WebCore::Chrome::scrollbarsModeDidChange const): Deleted.
* page/Chrome.h:
* page/ChromeClient.h:
* platform/HostWindow.h:

Source/WebKit:

* WebProcess/WebCoreSupport/WebChromeClient.cpp:
(WebKit::WebChromeClient::scrollbarsModeDidChange const): Deleted.
* WebProcess/WebCoreSupport/WebChromeClient.h:

Source/WebKitLegacy/mac:

* WebCoreSupport/WebChromeClient.h:

Source/WebKitLegacy/win:

* WebCoreSupport/WebChromeClient.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@221028 268f45cc-cd09-0410-ab3c-d52691b4dbfc