[FLINK-28330][runtime][security] Remove old delegation token framework code

[gaborgsomogyi]

Brief change log

Since the new delegation token framework works (it obtains/re-obtains/distributes tokens to task managers) it's time to remove the old code snippet which is only able to obtain tokens only at the initial phase. In this PR I've removed that code part.

Brief change log

• Removed old token fetch code
• KerberosDelegationTokenManager must only start in YARN when user provided valid credentials fix

Verifying this change

• Existing unit tests
• Manually on YARN and K8S (please see an example here)

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[gaborgsomogyi]

cc @mbalassi

[flinkbot]

CI report:

• ec95fb1 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[gaborgsomogyi]

@flinkbot run azure

[mbalassi]

LGTM, @gaborgsomogyi. I am verifying the change before merging locally.

[mbalassi]

nit: token manager, no valid

[mbalassi]

@gaborgsomogyi verified locally via the k8s operator. Will fix the typo and merge.