Remove duplicate imports in several places

Wrote a script to scan throught the python files in the repo,
and found the remaining duplicate imports in some python files like:
```
 from tensorflow.python.ops import random_ops
-from tensorflow.python.ops import random_ops
 from tensorflow.python.util.deprecation import deprecated
```
This fix removed all of them for duplicate imports.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>