Add function to remove file ending from file name

[fhightower]

HELP WANTED 👋 : If you'd like to take this challenge on, please let me know! Even if you're new to Python and/or github, this is a great place to start and I'd be happy to help walk you through this challenge as much as you need - don't hesitate to ask.

This particular issue will give you some exposure to writing a relatively simple function, working with strings in Python, and writing some tests.

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We already have a file_extension function to find a file extension. Now, we'd like to have a function which, given a file name (e.g. foo.py), returns the file name without the extension (e.g. foo). I propose the function should be named file_name_strip_extension, but am open to other suggestions.

If you're interested in taking this challenge on, comment on this issue and I'll assign it to you.