Re-group formula cells before we do recalc on load (for xlsx).

Change-Id: Iae6177433f05875e014de50eb4100fa381ddafdd
Move recalc on-load to after ScDocumentImport::finalize().

Doing this would avoid re-grouping formula cells twice.

Change-Id: I732658fc92f2fb3ddde0c0c00ae85f72074b6b48