autoboot: Drop unused CONFIG_MENUPROMPT

This is not defined by any board. We could use CONFIG_AUTOBOOT_PROMPT
instead perhaps, but this depends on CONFIG_AUTOBOOT_KEYED which is not
used for the single-key case.

So let's just remove CONFIG_MENUPROMPT.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/autoboot.c b/common/autoboot.c
index 012dd57..a6071ab 100644
--- a/common/autoboot.c
+++ b/common/autoboot.c
@@ -233,11 +233,7 @@
 	int abort = 0;
 	unsigned long ts;
 
-#ifdef CONFIG_MENUPROMPT
-	printf(CONFIG_MENUPROMPT);
-#else
 	printf("Hit any key to stop autoboot: %2d ", bootdelay);
-#endif
 
 	/*
 	 * Check if key already pressed
diff --git a/scripts/config_whitelist.txt b/scripts/config_whitelist.txt
index d06e2d2..2849441 100644
--- a/scripts/config_whitelist.txt
+++ b/scripts/config_whitelist.txt
@@ -1141,7 +1141,6 @@
 CONFIG_MEM_INIT_VALUE
 CONFIG_MEM_REMAP
 CONFIG_MENUKEY
-CONFIG_MENUPROMPT
 CONFIG_MENU_SHOW
 CONFIG_MFG_ENV_SETTINGS
 CONFIG_MIIM_ADDRESS