package/vdr-plugin-vnsiserver: don't install i18n files when not needed

package/vdr-plugin-vnsiserver: don't install i18n files when not needed

This used to cause a build failure with gettext-tiny, but this is now
fixed by the version bump in 160f0a033ba4edf2f7efe5fed82426acd3b34b70
("package/gettext-tiny: bump version"). Nevertheless, it makes sense
to not install the i18n files when they are not needed, i.e when
BR2_SYSTEM_ENABLE_NLS is disabled.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>