Remove dependencies from the codebase #196
Description
#194 removes the need for dependencies in action code, but does not delete them. This is intentional, to allow an orderly migration.
We should make an intermediate release to allow this migration, and then remove dependencies in the next LabThings release. This should include an audit of our codebase to get rid of dependencies used internally where appropriate. This probably includes ActionManagerDep, ActionManagerContextDep, and InvocationID (the last is still used in order to keep the other invocation-based dependencies working: it need not be used once they're gone).