HDDS-12955. Remove getCurrentContainerThreshold from SCMSafeModeManager

[erichung9060]

What changes were proposed in this pull request?

Removed getCurrentContainerThreshold from SCMSafeModeManager and updated its usage in StorageContainerManager.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-12955

How was this patch tested?

Pass all existing tests
https://github.com/erichung9060/ozone/actions/runs/16085692295

[nandakumar131]

@erichung9060, thanks for working on this.

Apart from unit tests, getCurrentContainerThreshold is used only by getSafeModeCurrentContainerThreshold which is exposed as JMX. The idea here is to not expose this metrics via StorageContainerManager class but via SafeModeManager.

We should properly define all the metrics that will be exposed by SafeModeManager and add this metrics over there if it's not already present and remove it from here.

Until we fix (or validate) all SafeModeManager metrics, I didn't want to remove this from here.

The code change that's done in this PR will not be necessary as we are planning on completely removing this method in future.