Remove deprecated object metrics from controllers

[darkowlzz]

In Flux v2.1, the object metrics (suspend and readiness) were deprecated from the flux controllers. See the deprecation notice in the metrics docs. See #4128 for detailed motivation and the recommended metrics collection strategy.

Since then, the newly refactored controllers have removed the deprecated metrics: helm-controller and image-automation-controller.
The same should now be removed from the rest of the controllers.

The following lists the controllers that should remove the deprecated metrics, it also includes the reconcilers that record these metrics with reference links to a few of them in their respective controller repositories:

• source-controller (for GitRepository, Bucket, HelmRepository, HelmChart and OCIRepository)
• kustomize-controller (for Kustomization)
• image-reflector-controller (for both ImageRepository and ImagePolicy)
• notification-controller (for Receiver only)

Following the above changes, the metrics docs page should be updated accordingly:

• Update metrics docs to remove the deprecation notice and alert at the top of the page (metrics docs source)

[stefanprodan]

To clarify, these are the deprecated metrics that are going to be removed:

• gotk_reconcile_condition
• gotk_suspend_status