Remove obsolete bookmarkManagerPrivate.canOpenNewWindows API function
The extension API function
chrome.bookmarkManagerPrivate.canOpenNewWindows was previously used to
disable opening new windows in Windows 8 Metro Mode. Now that mode is
removed, the function is essentially a no-op, as it always returns
true. Additionally, it is only used by one place in the bookmark
manager. This CL removes this obsolete function.