[SPARK-3281] Remove Netty specific code in BlockManager / shuffle

Netty functionality will be added back in subsequent PRs by using the BlockTransferService interface.

Author: Reynold Xin <rxin@apache.org>

Closes #2181 from rxin/SPARK-3281 and squashes the following commits:

5494b0e [Reynold Xin] Fix extra port.
ff6d1e1 [Reynold Xin] [SPARK-3281] Remove Netty specific code in BlockManager.
[SPARK-3285] [examples] Using values.sum is easier to understand than using values.foldLeft(0)(_ + _)

def sum[B >: A](implicit num: Numeric[B]): B = foldLeft(num.zero)(num.plus)
Using values.sum is easier to understand than using values.foldLeft(0)(_ + _), so we'd better use values.sum instead of values.foldLeft(0)(_ + _)

Author: Yadong Qi <qiyadong2010@gmail.com>

Closes #2182 from watermen/bug-fix3 and squashes the following commits:

17be9fb [Yadong Qi] Update CheckpointSuite.scala
714bda5 [Yadong Qi] Update BasicOperationsSuite.scala
57e704c [Yadong Qi] Update StatefulNetworkWordCount.scala
[SPARK-3190] Avoid overflow in VertexRDD.count()

VertexRDDs with more than 4 billion elements are counted incorrectly due to integer overflow when summing partition sizes. This PR fixes the issue by converting partition sizes to Longs before summing them.

The following code previously returned -10000000. After applying this PR, it returns the correct answer of 5000000000 (5 billion).

```scala
val pairs = sc.parallelize(0L until 500L).map(_ * 10000000)
  .flatMap(start => start until (start + 10000000)).map(x => (x, x))
VertexRDD(pairs).count()
```

Author: Ankur Dave <ankurdave@gmail.com>

Closes #2106 from ankurdave/SPARK-3190 and squashes the following commits:

641f468 [Ankur Dave] Avoid overflow in VertexRDD.count()
Better documentation for BlockObjectWriter.
Fix compilation error
Merge branch 'master' of github.com:apache/spark into fix-lz4-spilling