board: stm32mp1: remove bootdelay configuration for usb or serial boot

It is not allowed to change the user setting of bootdelay, so
remove the check of the boot-source to disable it dynamically
in board_late_init()

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/board/st/stm32mp1/stm32mp1.c b/board/st/stm32mp1/stm32mp1.c
index c64f20a..6873165 100644
--- a/board/st/stm32mp1/stm32mp1.c
+++ b/board/st/stm32mp1/stm32mp1.c
@@ -687,7 +687,6 @@
 
 int board_late_init(void)
 {
-	char *boot_device;
 #ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
 	const void *fdt_compat;
 	int fdt_compat_len;
@@ -735,11 +734,6 @@
 	board_check_usb_power();
 #endif /* CONFIG_ADC */
 
-	/* Check the boot-source to disable bootdelay */
-	boot_device = env_get("boot_device");
-	if (!strcmp(boot_device, "serial") || !strcmp(boot_device, "usb"))
-		env_set("bootdelay", "0");
-
 	return 0;
 }