Remove #! from non-executable files

[ekr-cfa]

I see that a number of the .py files start with #!/usr/bin/env/python, as in:

https://github.com/CDCgov/multisignal-epi-inference/blob/main/model/src/pyrenew/basic.py#L1

These are only needed when you will be executing the file directly, because their purpose is to tell the shell which interpreter to run. I.e., so you can do ./foo.py rather than python foo.py. However, if the python code is just a module that isn't intended to be run but just imported, then you don't need this.

In addition, this is actually the wrong line, because what's after the #! needs to be something executable, but this isn't usually a valid path, because /usr/bin/env is a program, not a directory. Rather, you want /usr/bin/env python, which runs the env command to run python.

[ghost]

Thanks for flagging that, @ekr-cfa. @dylanhmorris, I can address this on #26.