Prefer static_assert to verify in seccomp-filter

Prefer static_assert to verify in seccomp-filter

Prefer static_assert in just one file for now; the idea is to do
it elsewhere eventually.  static_assert is standard (starting with
C23) whereas verify is not, and static_assert can be used even in
pre-C23 files due to Gnulib’s support for it.
* lib-src/seccomp-filter.c: Do not include verify.h.
Prefer static_assert to verify.