## What changes were proposed in this pull request?

In the 2.0 document, Line "A full example that produces the experiment described in the PIC paper can be found under examples/." is redundant.

There is already "Find full example code at "examples/src/main/scala/org/apache/spark/examples/mllib/PowerIterationClusteringExample.scala" in the Spark repo.".

We should remove the first line, which is consistent with other documents.

## How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)

Manual test

Author: wm624@hotmail.com <wm624@hotmail.com>

Closes #13755 from wangmiao1981/doc.