Remove some purely external primops

The compiler doesn't create uses, nor emit in special ways the uses that exist already. These are just plain C-- FFI.

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

• are either individually buildable or squashed
• have commit messages which describe what they do (referring to Notes and tickets using #NNNN syntax when appropriate)
• have added source comments describing your change. For larger changes you likely should add a Note and cross-reference it from the relevant places.
• add a testcase to the testsuite.
• replace this message with a description motivating your change

If you have any questions don't hesitate to open your merge request and inquire in a comment. If your patch isn't quite done yet please do add prefix your MR title with WIP:.