Trimming dangling repeated nodes

[acampove]

Hi,

This PR reffers to #239 and is meant to:

• Make a few lines of code a little more readable.
• Trim nodes in the graph that arise from imports of functions from modules

[thebjorn]

You can run the tests locally by

pytest -vv --cov=pydeps tests

from tye pydeps directory.

ps: it's easier for me to merge a PR if it only contains changes needed to fulfill its purpose.