i2p: Removed from Debian

The i2p package is no longer in Debian, not even unstable: https://tracker.debian.org/pkg/i2p

However, I noticed some changes to the I2P wiki page: https://wiki.debian.org/I2P

that mention another package i2pd: https://tracker.debian.org/pkg/i2pd

It is being maintained, but we will need to evaluate if it's usable in FreedomBox, and can replace the old app.