Revert "Sign Fred releases and snapshots"

This reverts commit 9e16465c761e5b5a14d7101a158425c81682c9ec.

When freenet.jar is signed other jars that have classes in
"freenet.*" packages must also be signed. This means a new version of
freenet-ext would have to be signed and distributed, so I'm putting off
signing freenet.jar until a future release.