usb: gadget: Remove the legacy usbtty driver

The lone user of this driver has been removed for some time. Remove this
driver as well.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20250227205101.4127604-2-trini@konsulko.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 7e460f6..4f7de3e 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -294,13 +294,9 @@
 #if !CONFIG_IS_ENABLED(NS16550_MIN_FUNCTIONS)
 char ns16550_getc(struct ns16550 *com_port)
 {
-	while ((serial_in(&com_port->lsr) & UART_LSR_DR) == 0) {
-#if !defined(CONFIG_XPL_BUILD) && defined(CONFIG_USB_TTY)
-		extern void usbtty_poll(void);
-		usbtty_poll();
-#endif
+	while ((serial_in(&com_port->lsr) & UART_LSR_DR) == 0)
 		schedule();
-	}
+
 	return serial_in(&com_port->rbr);
 }