Clean up non-tm backends removal

[ptrus]

Some cleanup things todo, leftover by: #1806

• remove trivial scheduler
• remove backend flags wherever we are left with a single backend (if not done in: ABCI committee scheduler #1748)
• fix/re-enable discrepancy tests (done in: tests-e2e: discrepancy tests use deterministic beacon #1876)

[Yawning]

remove backend flags wherever we are left with a single backend

Since there is a non-trivial amount of inter-dependency between components and the consensus implementation, my thought here is:

• Add a consesus.backend flag that will set the beacon, keymanager, registry, roothash, scheduler, and staking backends (The consensus.backend flag can live under ekiden/cmd/common/flags).
• Possibly fold epochtime under the consensus.backend banner, and give epochtime/tendermint_mock the go/beacon: Remove the insecure beacon #1872 treatment (If the timekeeping code wasn't scheduled for a major refactor/rewrite, I would push harder for this).

The only component that isn't concretely tied to all other components and the consensus layer is storage at this point. I think having a single flag that controls the backend selection for all of the linked components is the right thing to do, ie: consesus.backend=tendermint).

[Yawning]

fix/re-enable discrepancy tests (if not done in: #1748)

All the nodes should have --beacon.debug.deterministic when running the discrepancy test.

[pro-wh]

remove backend flags wherever we are left with a single backend

Since there is a non-trivial amount of inter-dependency between components and the consensus implementation, my thought here is:

* Add a `consesus.backend` flag that will set the `beacon`, `keymanager`, `registry`, `roothash`, `scheduler`, and `staking` backends (The `consensus.backend` flag can live under `ekiden/cmd/common/flags`).

* Possibly fold `epochtime` under the `consensus.backend` banner, and give `epochtime/tendermint_mock` the #1872 treatment (If the timekeeping code wasn't scheduled for a major refactor/rewrite, I would push harder for this).

The only component that isn't concretely tied to all other components and the consensus layer is storage at this point. I think having a single flag that controls the backend selection for all of the linked components is the right thing to do, ie: consesus.backend=tendermint).

that'll be good. the tendermint stuff is really tightly coupled. I think yes on folding epochtime in, because all the other parts rely on it.

our backend APIs don't fit well with tendermint's processing model so it'll be less awkward when we don't have to handle that level of mixing and matching

[Yawning]

• Wire more things into the abci mux dependency thing. go/scheduler/tendermint/tendermint.go needs the tm beacon app as a "dependency", though if everything under consensus.backend=tendermint is understood to have implicit cross-dependencies, I'm not sure how useful the dependency mechanism is (since registering the apps should function regardless of ordering).

[Yawning]

The other parts of this are going into the time keeping cleanup I assume?

[ptrus]

yes (commented on the PR, forgot to also link here). The epochtime/time-keeping changes will be taken care of in: #1793