[DevTools] Remove V8Debugger::consoleMessagesCount.

third_party/WebKit/LayoutTests/http/tests/inspector-enabled/resources/console-clear-arguments-test.js

-function print(text)
-{
-    var output = document.getElementById("output");
-    var div = document.createElement("div");
-    div.textContent = text;
-    output.appendChild(div);
-}
-
-function dumpConsoleMessageCounts()
-{
-    var consoleMessageCount = window.internals.numberOfConsoleMessages(document);
-    if (consoleMessageCount === 3)
-        print("PASSED: found argument counts for 3 messages");
-    else
-        print("FAILED: unexpected number of messages: " + consoleMessageCount);
-
-    var consoleMessageWithArgumentsCount = window.internals.numberOfConsoleMessagesWithArguments(document);
-    if (consoleMessageWithArgumentsCount === 0)
-        print("PASSED: no messages with arguments");
-    else
-        print("FAILED: unexpected number of messages with arguments: " + consoleMessageWithArgumentsCount);
-}