Debian: Backport fixes from 0.9.30-4 package (ticket #2027)

and add buster files

* debian/NEWS: remove
* debian/README.Debian: update
* debian/compat: set compat level to 9.
* debian/control: added ${misc:Depends} to i2p & libjbigi-jni's Dep.
* debian/control: added bash-completion build dep
* debian/control: remove version on lsb-base dep
* debian/rules: fixed a typo (override_dh_dhlibdeps -> override_dh_shlibdeps).
* debian/rules: remove apps/susidns/src/lib/standard.jar symlink on clean.
* debian/i2p.postinst: Fixed a typo (missing ")" in /etc/default/i2p).