Remove literal #[unset!] cases
Remove literal #[unset!] cases

Ren/C forward belief is that there is no such thing as an unset
that can be stored in blocks...rather it is a transient state of evaluation
indicating a non-value.

This pre-emptively removes creations of #[unset!] (commit is pending
which disallows them)

metaeducation/ren-c-test,metaeducation/ren-c-test