### What changes were proposed in this pull request?
This patch proposes to fix the issue that storage memory is not decreasing even block is removed in BlockManager. Originally the issue is found while removed broadcast doesn't reflect the storage memory on driver/executors.
AppStatusListener expects the value of memory in events on block update as "delta" so that it adjusts driver/executors' storage memory based on delta, but when removing block BlockManager reports the delta as 0, so the storage memory is not decreased. `BlockManager.dropFromMemory` deals with this correctly, so some of path of freeing memory has been updated correctly.
### Why are the changes needed?
The storage memory in metrics in AppStatusListener is now out of sync which lets end users easy to confuse as memory leak is happening.
### Does this PR introduce any user-facing change?
No.
### How was this patch tested?
Modified UTs. Also manually tested via running simple query repeatedly and observe executor page of Spark UI to see the value of storage memory is decreasing as well.
Please refer the description of [SPARK-29055](https://issues.apache.org/jira/browse/SPARK-29055) to get simple reproducer.
Closes#25973 from HeartSaVioR/SPARK-29055.
Authored-by: Jungtaek Lim (HeartSaVioR) <kabhwan.opensource@gmail.com>
Signed-off-by: Marcelo Vanzin <vanzin@cloudera.com>
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