fdo#66969: Reset group dimension data from all referencing pivot objects.

The previous code was doing it only with the first referencing pivot table,
which would break the rest of them sharing the same cache if
the first one doesn't contain all group dimensions used in all of the
referencing pivot tables.

Change-Id: I35d6907ef8db7ed69db42583cac92b2b74406e2c
(cherry picked from commit b3977983e9f662392426f581516d86d7034ad0fd)
Reviewed-on: https://gerrit.libreoffice.org/7028
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>