✨ Do not expose sarif and policy command

[laurentsimon]

In order to simplify maintenance and support, we won't publicly advertise support for sarif and the score-based policy file.

1. sarif will be used internally for the action. Currently, we run the scorecard CLI; but long-term we may have a dedicated CLI for the action.
2. The policy file will be replaced by a setting-based policy file once we have finished separating checks from policy score-based policy calculation.

[github-actions]

Integration tests success for
[a29a107]
(https://github.com/ossf/scorecard/actions/runs/1604254532)

[github-actions]

Integration tests success for
[74010a0]
(https://github.com/ossf/scorecard/actions/runs/1604258981)

[github-actions]

Integration tests success for
[f2b54b3]
(https://github.com/ossf/scorecard/actions/runs/1604282020)

[laurentsimon]

same error as for my other PR:

> [internal] load metadata for docker.io/library/golang@sha256:3c4de86eec9cbc619cdd72424abd88326ffcf5d813a8338a7743c55e5898734f:
------
failed to solve with frontend dockerfile.v0: failed to create LLB definition: failed to authorize: rpc error: code = Unknown desc = failed to fetch oauth token: unexpected status: 503 Service Unavailable

Re-starting but I suppose it will fail again.
cc @azeemsgoogle @naveensrinivasan

[github-actions]

Integration tests success for
[9faa805]
(https://github.com/ossf/scorecard/actions/runs/1607832910)

[github-actions]

Integration tests success for
[bf582c1]
(https://github.com/ossf/scorecard/actions/runs/1607974666)