### What changes were proposed in this pull request?
`Worker#listTopDiskUseApps` should return `celeborn.metrics.app.topDiskUsage.count` applications.
### Why are the changes needed?
`Worker#listTopDiskUseApps` returns 2x `celeborn.metrics.app.topDiskUsage.count` application, which is not same as `celeborn.metrics.app.topDiskUsage.count` configuration at present. Meanwhile, `Worker#listTopDiskUseApps` reuses `StorageManager#topAppDiskUsage` method to get the top application list used for estimated application disk usage. Therefore, `Worker#listTopDiskUseApps` should return celeborn.metrics.app.topDiskUsage.count applications.
```
$ curl http://celeborn-worker:9096/listTopDiskUsedApps|grep used|wc -l
100
```
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
```
$ curl http://celeborn-worker:9096/listTopDiskUsedApps|grep used|wc -l
50
```
Closes#2668 from SteNicholas/CELEBORN-1547.
Authored-by: SteNicholas <programgeek@163.com>
Signed-off-by: mingji <fengmingxiao.fmx@alibaba-inc.com>