WHERE rules

Since nobody else is putting this on github, here we go....

Description of the proposal:
The ISG questionaire last year clarified that vendors are not parsing WHERE rules. It also clarified that WHERE rules are almost never needed in practical use cases (with a few exceptions).
Since the WHERE rules are not being used anyway, and are typical STEP/EXPRESS heritage, I suggest to remove them from the schema.
Specific cases that need additional restrictions will be looked at case-by-case.

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

What do we win:
Interoperability

What do we loose:
According to the ISG Questionnaire nothing in practice.

Schema impact:
Simpler

Instance model impact:
none

Backwards compatible:
no in theory, yes in practice because it is not used

Automatic migration possible:
yes, because files don't use it