roms: don't insert timeout.cfg

this is bloat, because it's something the user can already
do at runtime configuration anyway.

set it to a reasonable default of 8 seconds instead of 5,
and don't honour the timeout variable in target.cfg.

this will be documented in the next release.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/coreboot/hp8460pintel_8mb/target.cfg

@@ -3,5 +3,4 @@ xarch="i386-elf"
 payload_seabios="y"
 payload_seabios_withgrub="y"
 payload_memtest="y"
-grub_timeout=10
 grub_scan_disk="ahci"