Remove dead code

[rainest]

The existing PCS codebase contains several pieces of dead code under internal/. I decided to remove it after

From main as of fc206aa:

13:03:47-0700 baqytgul $ deadcode ./...
internal/api/api_test_setup_handler.go:37:6: unreachable func: CreateRouterAndHandler
internal/domain/power-status.go:168:6: unreachable func: PowerStatusMonitorStop
internal/domain/power-status.go:173:6: unreachable func: PowerStatusMonitorChangeInterval
internal/model/models.go:39:6: unreachable func: UUIDSliceEquals
internal/model/models.go:60:6: unreachable func: StringSliceEquals
internal/model/models.go:85:6: unreachable func: NewInvalidInputError
internal/model/models.go:90:6: unreachable func: Find
internal/model/power-status.go:76:29: unreachable func: PowerStateFilter.EnumIndex
internal/model/power-status.go:118:34: unreachable func: ManagementStateFilter.EnumIndex
internal/storage/distlock_etcd_impl.go:49:6: unreachable func: fromStorageETCD
internal/storage/distlock_mem_impl.go:51:6: unreachable func: fromStorageMEM

PowerStatusMonitorStop and PowerStatusMonitorChangeInterval: added in the initial version of power monitoring and never reachable. These are hypothetically useful, but that they've gone unused for 3y+ suggests they're YAGNI features.

Either can be handled in the cmd package instead. A PCS_POWER_SAMPLE_INTERVAL envvar is already available, and we can add a way to disable domain.PowerStatusMonitorInit() if desired.

internal/model/models.go contains generic utility functions added in the initial commit and never used. Most of these are handled by https://pkg.go.dev/golang.org/x/exp/slices. The file also contained two types that are only used by the API; these are now in the api package.

internal/model/power-status.go contained some unused utility function to convert an iota type to an int. These aren't useful, you can cast to an int if you really want to.

fromStorageETCD and fromStorageMEM have been left as-is. These exist because of poor interface design where StorageProvider and DistributedLockProvider aren't truly independent, and should be addressed as part of a larger refactor instead.

I did remove the DistributedLockProvider.InitFromStorage() functions, which were effectively dead for lack of non-test use.

[rainest]

@bmcdonald3 also worth considering for upstream, albeit less likely to be a concern for conflicts (insofar as this is all unused, I don't expect it to change in any CSM patches).

[alexlovelltroy]

@rainest Can we close this, or should we fix it up and get it merged? @shunr-hpe any feedback?

[cjh1]

We were waiting on the changes to be upstream, to avoid potential conflicts, however as @rainest points out its dead code so that is unlikely.

[shunr-hpe]

I'm ok with this change

[rainest]

Rebased to deconflict and add signoff:

• Removed models_test.go again. main had changed it to add the integration test build flag.
• Used main's transition_size_test.go. It made the same change to use Init() instead of InitFromStorage(), and also fixed a missing error return assign.