toradex: common: Remove stale function declaration

Remove stale show_boot_logo() declaration, not used anywhere.

Fixes: e6fd30dd9eef ("toradex: drop legacy show_boot_logo function and use splashscreen")
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
diff --git a/board/toradex/common/tdx-common.h b/board/toradex/common/tdx-common.h
index c96e875..d446e9f 100644
--- a/board/toradex/common/tdx-common.h
+++ b/board/toradex/common/tdx-common.h
@@ -12,8 +12,4 @@
 int ft_common_board_setup(void *blob, struct bd_info *bd);
 u32 get_board_revision(void);
 
-#if defined(CONFIG_DM_VIDEO)
-int show_boot_logo(void);
-#endif
-
 #endif /* _TDX_COMMON_H */