serial: Drop mention of SPL/TPL_SYS_MALLOC_F

These symbols do not (yet) exist, so drop the usage of them in the
serial Kconfig file. It has no effect.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 458f603..9f0f84c 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -160,7 +160,6 @@
 config SPL_DM_SERIAL
 	bool "Enable Driver Model for serial drivers in SPL"
 	depends on DM_SERIAL && SPL_DM
-	select SPL_SYS_MALLOC_F
 	default y
 	help
 	  Enable driver model for serial in SPL. This replaces
@@ -171,7 +170,6 @@
 config TPL_DM_SERIAL
 	bool "Enable Driver Model for serial drivers in TPL"
 	depends on DM_SERIAL && TPL_DM
-	select SYS_TPL_MALLOC_F
 	default y if TPL && DM_SERIAL
 	help
 	  Enable driver model for serial in TPL. This replaces