Remove purely external primops

The compiler doesn't create uses nor compiles the uses that exist
specially. These are just plain C-- FFI.

These `await*` ones are especially important to so convert because "true"
primops are hard to make platform-specific currently.

The other exports are part of this commit so this module always exports
something, which avoids silly CPP elsewhere. More will be added later
once `foreign import prim` is extended.