Remove obsolete Python 2.x scripting support

[carlosame]

The echosvg-script module supports Python 2.x scripting (which is disabled by default) via the jython package, but that package is obsolete and gets in the way of full modularisation. Quoting from #8 (comment):

The obsolete Python 2.x scripting seems an obvious target for removal: nobody is going to pay jython developers to implement Python 3.x (all the resources in that area are being dropped into GraalVM) and that 3.x upgrade is too big for the volunteer developers working in their spare time (see jython/jython/issues/24).

So removing the support for the superseded Python 2.x scripting seems appropriate.