USB: remove warn() macro from usb.h

USB should not be having it's own printk macros, so remove warn() and
use the system-wide standard of dev_warn() wherever possible.  In the
few places that will not work out, use a basic printk().

Now that all in-tree users are gone, remove the macro.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

include/linux/usb.h

@@ -1744,8 +1744,6 @@ extern void usb_unregister_notify(struct notifier_block *nb);
 	format "\n" , ## arg)
 #define info(format, arg...) printk(KERN_INFO KBUILD_MODNAME ": " \
 	format "\n" , ## arg)
-#define warn(format, arg...) printk(KERN_WARNING KBUILD_MODNAME ": " \
-	format "\n" , ## arg)
 
 #endif  /* __KERNEL__ */