Delete requirements.txt

[pllim]

It is unclear to me what this is useful for. You should pull requirements from setup requirements. Build, install, test, docs requirements should all be separated and not mixed up like this.

https://github.com/spacetelescope/pysiaf/blob/master/requirements.txt

[pllim]

You also don't need https://github.com/spacetelescope/pysiaf/blob/master/docs/requirements.txt

Everything can be pulled from setup if you define it correctly.