treewide: drop unused meta-security layer

This was added with cde0f094 for libseccomp, but shortly after that
upstream moved libseccomp from meta-security to core (241c7d2e6).  As
such, meta-security is no longer used or required.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Change-Id: I371e54b11f6336720dfc6edf0ef733d22b7fb4f2