[improve][broker] Clean up config changes without a PIP since the 4.0 LTS

[BewareMyPower]

• Remove managedLedgerOffloadReadThreads from https://github.com/apache/pulsar/pull/24025
• Remove managedLedgerMaxReadsInFlightPermitsAcquireTimeoutMillis and managedLedgerMaxReadsInFlightPermitsAcquireQueueSize from https://github.com/apache/pulsar/pull/23901
• Remove managedLedgerCursorResetLedgerCloseTimestampMaxClockSkewMillis from https://github.com/apache/pulsar/pull/22792 The configs above only increase the complexity and are hard to configure.

Add more comments to managedLedgerPersistIndividualAckAsLongArray from https://github.com/apache/pulsar/pull/23759. This config was added to keep the compatibility from 3.x or earlier so it has value to retain. 3.x users must configure it with false when upgrading to 4.0.

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

Matching PR in forked repository

PR in forked repository:

[BewareMyPower]

That's the whole point of the managedLedgerMaxReadsInFlightSizeInMB solution that it adds a limit.

Just a simple question. When should users modify this config?

[BewareMyPower]

In many cases, it will be useful if the value can be modified if a user faces an issue that could be solved by tuning the limit.

The key point is, since there are too many configurations, it's impossible for users to tune configs one by one. Back to the example of https://github.com/apache/pulsar/pull/23901, how can users realize the issue is related to the asynchronous InflightReadsLimiter?