Remove criteria F

[twof]

Criteria F is a duplicate of Criteria C and is overly vague

[benjie]

F is not a duplicate of C, which is demonstrated by the evaluations for them differing - both proposal 2 and 4 fail criteria C (clarified in #1659), but for F proposal 2 is consistent because in a new schema with @strictNullability, Int always means "semantically non-nullable". Proposal 4 fails criteria F because it has two modes of operation on the same schema, and Int means essentially opposite things in these two modes: either nullable or non-nullable depending on the mode. Perhaps rather than removing this you can help reword it to make the difference clearer?