cli: fix setting "serial.parity" enum

The meta data type descriptor must set .get_gtype only for
GObject properties which are of type int or uint. That is, when
the enum type cannot be automatically detected.

However, NM_SETTING_SERIAL_PARITY is a g_param_spec_enum()
of type NM_TYPE_SETTING_SERIAL_PARITY, so setting the get_gtype()
hook is wrong and leads to a crash

   $ /bin/nmcli connection add type gsm autoconnect no con-name t ifname '*' apn xyz serial.parity 5

   (process:11086): libnmc-CRITICAL **: 15:04:35.180: file clients/common/nm-meta-setting-desc.c: line 1283 (_set_fcn_gobject_enum): should not be reached
   Segmentation fault (core dumped)

That is because the enum property setter does:

    »···if (   has_gtype
    »···    && NM_IN_SET (gtype_prop,
    »···                  G_TYPE_INT,
    »···                  G_TYPE_UINT)
    »···    && G_TYPE_IS_CLASSED (gtype)
    »···    && (gtype_class = g_type_class_ref (gtype))
    »···    && (   (is_flags = G_IS_FLAGS_CLASS (gtype_class))
    »···        || G_IS_ENUM_CLASS (gtype_class))) {
    »···»···/* valid */

meaning, it only allows "has_gtype" if the native "gtype_prop" is
G_TYPE_INT or G_TYPE_UINT.

Fixes: 9a68123827

clients/common/nm-meta-setting-desc.c

@@ -7152,7 +7152,6 @@ static const NMMetaPropertyInfo *const property_infos_SERIAL[] = {
 		.property_type =                &_pt_gobject_enum,
 		.property_typ_data = DEFINE_PROPERTY_TYP_DATA (
 			PROPERTY_TYP_DATA_SUBTYPE (gobject_enum,
-				.get_gtype =            nm_setting_serial_parity_get_type,
 				.value_infos =          ENUM_VALUE_INFOS (
 					{
 						.value = NM_SETTING_SERIAL_PARITY_EVEN,