port to androguard >= 4 and drop support for older than 3.3.5

This also makes androguard a hard requirement, which has been true for a while anyway. So the code that handles androguard as an optional requirement is removed. androguard from Debian/buster is new enough, so this does not seem like it will cause any problems.

For a long time, androguard was barely maintained, so it wasn't worth thinking about new versions. Now with 4.x, it is actively developed again.

Debian/bullseye and Ubuntu/20.04/focal both include new enough versions. Debian/buster's is too old (3.3.3).