javaexec-script: Remove support for 'gij'. * build-aux/javaexec.sh.in: Don't test HAVE_GIJ. * m4/javaexec.m4 (gt_JAVAEXEC): Don't set HAVE_GIJ. Don't set CONF_JAVA to 'gij'. * m4/javacomp.m4: Update comment.