purge aapt requirements and elevate apksigner
This removes aapt parsing code everywhere where it can be entirely replaced by androguard v3.3.3+. aapt support is still included as an opportunistic fallback for reading the Application ID and Version Code from APKs. APKs can do some very weird things, at the very least,
fdroid update should be able to find their Application ID and Version Code.
fdroid init then prioritizes finding apksigner and enabling that so that v2/v3 signatures verify.
More details in the commit messages. I'm running a test of the buildserver changes on verification.