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.

testing/scripts/recipes/013_strongswan.mk

@@ -63,7 +63,6 @@ CONFIG_OPTS = \
 	--enable-attr-sql \
 	--enable-mediation \
 	--enable-botan \
-	--enable-blowfish \
 	--enable-kernel-pfkey \
 	--enable-integrity-test \
 	--enable-leak-detective \