tpm2: Remove redundant methods from the Connection API.

With the introduction of the `efi/preinstall` sub-package and the `RunChecks` API (and later on, the `RunChecksContext` API), some methods of the `Connection` API feel like they should eventually become redundant, eg:

- `Connection.IsEnabled` - this is something that the pre-install tests already do.
- `Connection.LockoutAuthSet` - the pre-install tests check that the TPM is not in DA lockout mode (although there's no way to check that the lockout hierarchy is locked out other than by using it) and it also ensures that the authorization values for the storage, endorsement and lockout hierarchies are all empty.