removed error raising when calling warn

[shimwell]

I triggered this warn statement and noticed that the raise in front of the warn causes the program to terminate with and error stating one can only raise errors. I believe warn should not be raised like we have elsewhere in the code.

Fixes # (issue)
code having fatal error when it should just warn user

Checklist

• I have performed a self-review of my own code
• I have followed the style guidelines for Python source files (if applicable)