USB: remove USB HUB entry from MAINTAINERS

Digging through old mail, I found a note about needing to remove the
separate entry for the USB HUB driver.  It's not been separable from
usbcore (host side!) since quite early in the 2.4 kernel series.
And Johanness certainly isn't involved with it any more.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>