Improve PyPI malware detector to reduce false positives

[Yao-Wen-Chang]

Currently, the PyPI malware detector using seven heuristics generates a high number of false positives.
To enhance the accuracy of our detection, I suggest extending the check to
further confirm malicious behavior within the entire source code and highlight suspicious code blocks.

[behnazh-w]

This PR removes the heuristics that introduce too many FPs: #797

We should definitely improve and expand on the source-code analysis though.