Repeated Kind is OK, but repeated Type is not

[chaudhuri]

As of 5bb9833, Kind declarations can be repeated with no warnings or errors.

Kind n type.
Kind n type. % no issues

However, Type declarations cannot be repeated.

Type z n.
Type z n.

Error: Predicate or constant z already exists

Seems like an unintended discrepancy. Should perhaps be fixed by allowing redeclarations of Types as well.

(Issue spotted in discussion with @innofarah.)