[SPARK-16403][EXAMPLES] Cleanup to remove unused imports, consistent style, minor fixes

## What changes were proposed in this pull request?

Cleanup of examples, mostly from PySpark-ML to fix minor issues:  unused imports, style consistency, pipeline_example is a duplicate, use future print funciton, and a spelling error.

* The "Pipeline Example" is duplicated by "Simple Text Classification Pipeline" in Scala, Python, and Java.

* "Estimator Transformer Param Example" is duplicated by "Simple Params Example" in Scala, Python and Java

* Synced random_forest_classifier_example.py with Scala by adding IndexToString label converted

* Synced train_validation_split.py (in Scala ModelSelectionViaTrainValidationExample) by adjusting data split, adding grid for intercept.

* RegexTokenizer was doing nothing in tokenizer_example.py and JavaTokenizerExample.java, synced with Scala version

## How was this patch tested?
local tests and run modified examples

Author: Bryan Cutler <cutlerb@gmail.com>

Closes #14081 from BryanCutler/examples-cleanup-SPARK-16403.

1 files changed, 0 insertions, 1 deletions

diff --git a/examples/src/main/python/streaming/queue_stream.py b/examples/src/main/python/streaming/queue_stream.py
index b3808907f7..bdd2d48519 100644
--- a/examples/src/main/python/streaming/queue_stream.py
+++ b/examples/src/main/python/streaming/queue_stream.py
@@ -22,7 +22,6 @@
  To run this example use
     `$ bin/spark-submit examples/src/main/python/streaming/queue_stream.py
 """
-import sys
 import time
 
 from pyspark import SparkContext