gpredict: properly configure perl for intltool

Also remove dependency on p5.28-xml-parser since intltool
takes care of these perl dependencies for you.

This is probably overkill but at least it allows configure to report
the right perl (${prefix}/bin/perl5.28 instead of /usr/bin/perl).

No need for a rev-bump since there are no changes in the installed files.

science/gpredict/Portfile

@@ -33,9 +33,11 @@ use_bzip2           yes
 perl5.branches      5.28
 
 depends_build       port:intltool \
-                    port:p${perl5.major}-xml-parser \
                     port:pkgconfig
 depends_lib         port:goocanvas2 \
                     port:curl
 
+configure.env-append \
+                    INTLTOOL_PERL=${perl5.bin}
+
 livecheck.regex     ${name}-(\[0-9.\]+)${extract.suffix}