Revert inadvertent modification of type_reference/offapi.idl

...from 9835bb562cfe3a5d386c24d86176ba7bb5ab26d2 "MM: export the SwDocShell mail
merge via UNO."  It shall only be edited manually when deliberately going
incompatible.

Change-Id: I19c82dca3b6537631a155629d6072b516b32ded5