usb: Drop old non-DM code

The driver model deadline for USB was in 2019, so drop the old USB
keyboard code, to avoid needing to deal with the extra code path.

Drop the unnecessary #ifdef around USB_KBD_BOOT_REPORT_SIZE while we
are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/usb/Kconfig b/drivers/usb/Kconfig
index a972d87..311aaa7 100644
--- a/drivers/usb/Kconfig
+++ b/drivers/usb/Kconfig
@@ -99,7 +99,8 @@
 
 config USB_KEYBOARD
 	bool "USB Keyboard support"
-	select DM_KEYBOARD if DM_USB
+	depends on DM_USB
+	select DM_KEYBOARD
 	select SYS_STDIO_DEREGISTER
 	---help---
 	  Say Y here if you want to use a USB keyboard for U-Boot command line