Fix some bug risks and code quality issues

[mohi7solanki]

Changes:

• Remove unnecessary list comprehension
• Set value instead of comparison in tpot_tests.py
• Remove useless print statement
• Fix C style iteration in _operator_count
• Add .deepsource.toml file to file to run continuous static analysis on
  the repository with DeepSource

This PR also adds .deepsource.toml configuration file to run static analysis continuously on the repo with DeepSource. Upon enabling DeepSource, quality and security analysis will be run on every PR to detect 500+ types of problems in the changes — including bug risks, anti-patterns, security vulnerabilities, etc.

DeepSource is free to use for open-source projects, and is used by teams at NASA, Uber, Slack among many others, and open-source projects like ThoughtWorks/Gauge, Masonite Framework, etc.

To enable DeepSource analysis after merging this PR, please follow these steps:

• Sign up on DeepSource with your GitHub account and grant access to this repo.
• Activate analysis on this repo here.
• You can also look at the docs for more details. Do let me know if I can be of any help!

Questions:

• Do the docs need to be updated? - NO
• Does this PR add new (Python) dependencies? - NO

[weixuanfu]

Thank you for the fixes and suggestion of DeepSource. I will merge this PR to dev branch for now. I checked the DeepSource report from your forked repo, it seems tpot need a lot of code cleaning but some of major code issues may be not valid. We will check the docs of DeepSource and also clean TPOT codes before merging it to master branch.

[mohi7solanki]

@weixuanfu thanks for merging, you can report false positives on the platform if you find any, we will try to fix them right away or ping me at mohit@deepsource.io for any queries/suggestions.