Remove external dependencies

This removes the file and ssdeep dependencies from the source tree.
These dependencies are available in distro repositories and should not be embedded as this leads to various issues.

The deps.sh script has been updated to install these packages. The other two C libraries, which are fairly obscure, remain in the source tree.

autoreconf will have to be run. (Ideally, ./configure should be kept out of the repo via .gitignore and only provided in release tarballs.)