Remove support of `reject_old_samples` and `reject_old_samples_max_age` in favour of Out Of Order Samples support

[alvinlin123]

We are likely to release out of order sample support in Release 1.15, which deprecates reject_old_samples and reject_old_samples_max_age. As promised in https://cortexmetrics.io/docs/configuration/v1guarantees/, we will keep the deprecated flags for 2 minor releases, so we will remove the 2 flags in release 1.17.

[yeya24]

Based on the dicussion from #4964, the new OOO feature cannot cover all use cases of reject_old_samples and reject_old_samples_max_age so let's not deprecate these flags for now.