[SPARK-15492][ML][DOC] Binarization scala example copy & paste to spark-shell error

## What changes were proposed in this pull request?

(Please fill in changes proposed in this fix)
The Binarization scala example val dataFrame : Dataframe = spark.createDataFrame(data).toDF("label", "feature"), which can't be pasted in the spark-shell as Dataframe is not imported. Compared with other examples, this explicit type is not required.

So I removed Dataframe in the code.
## How was this patch tested?

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

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

Closes #13266 from wangmiao1981/unit.