de-macroize XINTERFACE_DECL

Change-Id: Iaa1cf999189f6b62547c208eadc38150400ca0fe
Reviewed-on: https://gerrit.libreoffice.org/8454
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>