[cleanup][broker] Follow up on #16968 to restore some behavior in PersistentDispatcherMultipleConsumers class

[mattisonchao]

Motivation

PR #16968 made changes to the logic how sendInProgress field is set in PersistentDispatcherMultipleConsumers class and a decision was made in a post-merge review to revert the changes.

Modifications

• Fix typo.
• Revert irrelevant code.

Verifying this change

• [x] Make sure that the change passes the CI checks.

Documentation

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