Remove COMPAT_FREEBSD4/5/6/7/9 from MINIMAL and FIRECRACKER kernel configurations

FIRECRACKER is not a legacy config, so remove the really old FreeBSD
versions from it. MINIMAL has a similar history, and limited target
audience which has little to no overlap with really old binaries. Either
of these is really easy to get additional binary compat with the include
directive, so balance things better. Leave GENERIC alone.

PR: 231768
Signed-off-by: Henrich Hartzer <henrichhartzer@tuta.io>
Reviewed by: imp (MINIMAL), cperciva (FIRECRACKER)
Pull Request: https://github.com/freebsd/freebsd-src/pull/1228