Set split proportions to None if split column is provided

[ejm714]

If a user just provides a split column, they'll get the default split proportions. This leads to the message

Labels contains split column yet split_proportions are also provided. Split column in labels takes precedence.

which is a bit confusing if a user doesn't intentionally provide split proportions. It'd be nice if we detect splits in the labels csv to set split proportions to None, so that this warning only shows up if a user intentionally provides both.

This won't change underlying behavior, just make the logging more intuitive.

[aaronphilip19]

Hey, @sambujangfofana and I are students from the University of Michigan. We are currently working on a project wherein we have to contribute to a Github repository(https://eecs481.org/hw6.html). We are pretty interested in this issue and would want to work on it. We hope to submit a pull request this week. Could we be assigned this issue?