Simplify the WebKitLegacy menu conversion code

Simplify the WebKitLegacy menu conversion code
https://bugs.webkit.org/show_bug.cgi?id=150509

Reviewed by Andreas Kling.

Source/WebKit/mac:

* WebCoreSupport/WebContextMenuClient.mm:
(fixMenusToSendToOldClients):
(fixMenusReceivedFromOldClients):
(WebContextMenuClient::getCustomMenuFromDefaultItems):

Tools:

Implement the context menu delegate method so we'll test that code path.

* MiniBrowser/mac/WK1BrowserWindowController.m:
(-[WK1BrowserWindowController webView:contextMenuItemsForElement:defaultMenuItems:]):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@191512 268f45cc-cd09-0410-ab3c-d52691b4dbfc