bug#53484: 29.0.50; Removing libseccomp-dev 2.5.1-1~bpo10+1 allows emacs to compile

[Philipp Stephani]

> Am 24.01.2022 um 22:56 schrieb Glenn Morris <rgm@gnu.org>:
> 
> 
> I note that the required version of libseccomp in emacs-28 (2.5.2) is
> now greater than that found in eg rhel 8.5 (2.5.1). So there are some
> platforms where libseccomp support was working in earlier emacs-28
> pretests but is now absent.

Note that this only refers to the construction of the seccomp filter that we 
build for convenience.  The Emacs binary itself and the actual seccomp 
sandboxing mechanism doesn't depend on libseccomp.  Users that don't have 
libseccomp or an older version will still get the seccomp support, just not the 
specific filter file that we provide.