Fix the LGTM issues

[cclauss]

The LGTM service is run by Travis CI on all pull requests and it currently reports:

2 Errors
12 Warnings
10 Recommendations

https://lgtm.com/projects/g/TheAlgorithms/Python/alerts/?mode=list

Please try to fix just a few of these issues in a pull request.

For speed of review, please do not try to do them all. Where possible add doctests as well.

[cclauss]

@epicalyx, @harshildarji, @rishu2403 Could one of you please consider fixes to unused variables in logistic_regression? They might be false positives or they might be worth fixing.

[AmritK10]

I would like to work on the issue of unused variables in logistic_regression.

[cclauss]

Go for it!