Avoid creating a <complexFaultRupture> with multiple <complexFaultGeometry> definitions

[raoanirudh]

The engine no longer supports this after gem/oq-engine#5443, and users keep running into this issue:

• complexFaultRupture does not recognize multiple <complexFaultGeometry> definitions oq-engine#5440
• complexFaultRupture error, too many values to unpack? oq-engine#8278
• openquake-users/c/o3lsEp4qOyI/m/N5uTEhdvAgAJ