fdo#75757: remove inheritance to std::vector

from PhoneticPortionModelList.

Change-Id: I0972bb1bac93e86cb73b9e03af11a84b06e177be
Reviewed-on: https://gerrit.libreoffice.org/11269
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>