blowfish: Remove legacy Blowfish implementation

There is no reason to use Blowfish nowadays.  Given that there are some
other plugins that still provide it, there is especially no reason to
maintain this custom implementation.  Also removed the two test scenarios
that used the plugin to avoid promoting the use of this algorithm.

LICENSE

@@ -1,5 +1,5 @@
-Except for code in the blowfish, des, md4 and md5 plugins (see below) the
-following terms apply:
+Except for code in the des, md4 and md5 plugins (see below) the following
+terms apply:
 
 For copyright information see the headers of individual source files.