A while ago I repackaged a small tool that helps cleaning up old plugin
versions after designer AU updates in order to improve load times and disk
usage. Work nicely on Windows, but not on Linux, though. Now I came across
another tool that seems to work on LInux, too:

Just drop the JAR file into the Designer install folder and run

<path to a jre_1.7.x>/bin/java -jar
plugin-cleaner-0.4-jar-with-dependencies.jar --test --mode unlimited

to get a list of outdated plugins found. Leave out the --test parameter to have
the tool move all found plugins into a folder named duplicates-<timestamp> that
you can then inspect and delete if you wish. Try the --help parameter for some
options that might be useful.

The released JAR is compiled with java 1.7, so running it with the v1.6 java
that comes with Designer does not work.