Make all dependencies non-optional/remove

[rvansa]

Currently the build checks for libbsd and libnftables development files in the build environment and if these are present the binary depends on the libraries. This creates some trouble if built in one environment and executed in another.

Let's do one of the possibilities below:

1. Never depend on those (regardless if present in the system)
2. Link to those libraries statically
3. Always depend on those

Based on CRaC/container-images#4 (comment) 1) or 2) would be the correct option, and 1) is certainly less work.

[jankratochvil]

Fix docker image missing shared libraries #11