[SPARK-3709] Executors don't always report broadcast block removal properly back to the driver (for branch-1.1)

Author: Reynold Xin <rxin@apache.org>

Closes #2591 from rxin/SPARK-3709-1.1 and squashes the following commits:

ab99cc0 [Reynold Xin] [SPARK-3709] Executors don't always report broadcast block removal properly back to the driver