Remove transitive dependency 'sqlparse' from requirements.txt

[vtalos]

As part of our ongoing research on Python dependency management we noticed a potential improvement in your project’s dependency management.

Specifically, the transitive dependency sqlparse, which is required by Django, is specified as a requirement in the requirements.txt file, even though it is not used directly and does not need to be listed explicitly.

This PR removes it from requirements.txt to let pip manage it automatically, which helps keeping the dependency list clean.

Hope this is helpful!