Drop scenarios from the user-facing SDK

For 2.0 we want our users to use Daml Script instead. We have lots of tests and internals that rely on scenarios so as a first step, we should only drop it from the user facing SDK.

I’d suggest the following steps:

1. Add a hidden flag to damlc to control whether scenarios are supported or not. If scenario support is off we error out when compiling scenarios with an error message suggesting to users to use Daml Script instead. It’s fine if that flag is available to users in the resulting SDK as long as it does not show up in --help. We can start with keeping scenario support on by default and then gradually switch it off in places until we can flip the default.
2. The script/scenario service should gain a flag that enables/disables scenario support. If it is disabled we reject grpc requests to start scenarios (but continue accepting requests for scripts). Apart from tests the script service is always started from damlc so it should pass that flag depending on its own mode.

We can then later start switching over our own tests and eventually kill that flag but we don’t have to do that on a 2.0 timeline.

[cocreature]

Let’s keep this open until we flipped the default.

[cocreature]

Yep, thanks a lot for taking care of this!