[SPARK-17525][PYTHON] Remove SparkContext.clearFiles() from the PySpark API as...

[SPARK-17525][PYTHON] Remove SparkContext.clearFiles() from the PySpark API as it was removed from the Scala API prior to Spark 2.0.0

## What changes were proposed in this pull request?

This pull request removes the SparkContext.clearFiles() method from the PySpark API as the method was removed from the Scala API in 8ce645d4. Using that method in PySpark leads to an exception as PySpark tries to call the non-existent method on the JVM side.

## How was this patch tested?

Existing tests (though none of them tested this particular method).

Author: Sami Jaktholm <sjakthol@outlook.com>

Closes #15081 from sjakthol/pyspark-sc-clearfiles.

python/pyspark/context.py

@@ -787,14 +787,6 @@ class SparkContext(object):
         """
         self._jsc.sc().addFile(path)
 
-    def clearFiles(self):
-        """
-        Clear the job's list of files added by L{addFile} or L{addPyFile} so
-        that they do not get downloaded to any new nodes.
-        """
-        # TODO: remove added .py or .zip files from the PYTHONPATH?
-        self._jsc.sc().clearFiles()
-
     def addPyFile(self, path):
         """
         Add a .py or .zip dependency for all tasks to be executed on this