Remove CipherUtils.

We haven't used this in the N years it's existed, and it uses
scary MD5/DES stuff.

Change-Id: I3934d3cc769980527f03b16a5c273f76fc89cdfb
Reviewed-on: http://gerrit.dmdirc.com/3948
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager