[FLINK-36979][rpc] Reverting pekko version bump in Flink 1.19

[XComp]

This reverts commit de44f60.

What is the purpose of the change

Reverts the pekko version bump that includes an upgrade to netty 4.x. Corresponding discussion happened in FLINK-36510.

Brief change log

• Plain revert

Verifying this change

• no additional verification done aside from CI

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

• Dependencies (does it add or upgrade a dependency): yes
• 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: yes
• 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

[flinkbot]

CI report:

• 0a0b714 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

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

[afedulov]

The Pekko folks could not reproduce this leak outside of Flink, so it is ultimately up us to help localize the issue as we cannot expect the fix to come from the Pekko side alone:
apache/pekko#1634

@ferenc-csaky could you investigate a bit according to the advice we received?
https://issues.apache.org/jira/browse/FLINK-36510?focusedCommentId=17908999&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-17908999

[afedulov]

@ferenc-csaky just saw your comment on the symmetric 1.20 revert PR, glad to see you are on it :)

[He-Pin]

try -Dio.netty.tryReflectionSetAccessible=true to make it work smooth on Java 9+
with -Dio.netty.allocator.type=unpooled to make it keep the old unpooled behavior.

[ferenc-csaky]

Opened #25956 which I believe should supersede this current PR.

[davidradl]

@ferenc-csaky can we close this PR?

[XComp]

fyi: I responded in the related 1.20 PR regarding the state of this PR.

[XComp]

Closing this PR as it is superseded by FLINK-37100