Remove Aast.TCPartiallyAbstract
Summary: Removes the Aast structure for partially abstract type constants. Now, any constant without abstract lowers into `TCConcrete`. I moved the definition error to the parser but retained the code / error message as we may want to allow `as` constraints back on concrete type constants now that the concept of partially abstract type constants has been eliminated.
Reviewed By: andrewjkennedy
Differential Revision:
D31328780
fbshipit-source-id:
923172c6dc0c7567ee1b5e894ee845eb2a8cb703