#364 spatial spec example problematic

[Frank Bergmann]

The example at spatial/specification/examples/sampledfield_asnt.xml is problematic, in that

• the id'imgvals is used twice for a parameter and a sample field
• the initial assignment uses the id of the geometry img, rather than the sample field (or parameter) imgvals

[Lucian Smith]

Moved to https://github.com/sbmlteam/sbml-specifications/issues/362