lib/romstage_stack.c: Remove file

After platforms have moved to POSTCAR_STAGE=y the only
remaining user is binaryPI now. Make it simpler.

Change-Id: Ia70c5c85e06c42f965fb7204b633db9b619e2e84
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33957
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/include/program_loading.h

@@ -173,10 +173,6 @@ void run_romstage(void);
 /* Run ramstage from romstage. */
 void run_ramstage(void);
 
-/* Determine where stack for ramstage loader is located. */
-enum { ROMSTAGE_STACK_CBMEM, ROMSTAGE_STACK_LOW_MEM };
-uintptr_t romstage_ram_stack_base(size_t size, int src);
-
 /* Backup OS memory to CBMEM_ID_RESUME on ACPI S3 resume path,
  * if ramstage overwrites low memory. */
 void backup_ramstage_section(uintptr_t base, size_t size);