Deprecate IfcExternalSpatialStructureElement and subtype

[SergejMuhic]

Description of the proposal:

Describe how it contributes to the objectives set in https://github.com/buildingSMART/NextGen-IFC/wiki/Towards-a-technology-independent-IFC:

What do we win: Spatial Structure element that has not been used. What do we loose nothing Schema impact: low Instance model impact: non existant Backwards compatible: yes Automatic migration possible: yes Additional implications: can be modeled with IfcSpace.EXTERNAL at IfcSpace level and IfcFacility and IfcFacilityPart on higher levels

Note that not all points need to be satisfied! Backwards compatibility and file size are not concerns.

[Moult]

Agree.