Add missing map tests

[mlevesquedion]

This PR adds (currently failing) tests for MapUpdate as well as the delete operation on maps.

Specifically, this adds three (negative) cases:

• Deleting a key (delete(map, key)) from a map does not taint the key
• Updating a map with a tainted value (map[key] = value) does not taint the key
• Updating a map with a tainted key (map[key] = value) does not taint the value

The first case exercises some behavior involving Call instructions.

The 2nd and 3rd cases validate that when propagating to a MapUpdate operation, only the Map is tainted (the positive case is already covered by other tests).

This PR is a precursor to #178.

• Tests pass
• (N/A) [ ] Running against a large codebase such as Kubernetes does not error out.
• (N/A) [ ] Appropriate changes to README are included in PR