instead of a hand-coded equivalent. Note that I can't use
std::unique_ptr, because the parsing code appears to just randomly leak
AstScope

Change-Id: Idc56dfe1f084db55c9d5a7558ac44ddab53b98e3
Reviewed-on: https://gerrit.libreoffice.org/59771
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>