Remove js as language from configure.ac

* configure.ac: Remove js language.

It does not make much sense to integrate gpgme-js into the
GPGME build system. gpgme-js will be distrbuted by it's users
as part of the web extensions / their distribution as that
is the JavaScript way.

So they can use their tools etc. to compile gpgme-js JavaScript
style, which is documented in the lang/js folder.