Remove default value of CONFIG_PREBOOT for CONFIG_USB_STORAGE

Remove the default value "usb start" for CONFIG_USB_STORAGE as the USB
storage boot initialization is correctly managed by  distro boot command
('usb_boot' defined in include/config_distro_bootcmd.h already include
the command 'usb  start').

Fixes: 324d77998ed6 ("Define default CONFIG_PREBOOT with right config option")
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig.boot b/common/Kconfig.boot
index 4191bfb..522f5f3 100644
--- a/common/Kconfig.boot
+++ b/common/Kconfig.boot
@@ -880,7 +880,7 @@
 config PREBOOT
 	string "preboot default value"
 	depends on USE_PREBOOT && !USE_DEFAULT_ENV_FILE
-	default "usb start" if USB_KEYBOARD || USB_STORAGE
+	default "usb start" if USB_KEYBOARD
 	default ""
 	help
 	  This is the default of "preboot" environment variable.