Fixed the expectation that porter would already be installed

[dgannon991]

What does this change

It allows for installing porter on a fresh system from source code

What issue does it fix

Closes #3032

Notes for the reviewer

I manually tested changing the permissions on ~/.porter/porter to ensure it threw an error it the binary existed but couldn't be removed, however I do not have access to an apple mac to confirm the original issue it was attempting to fix is still OK.

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR

[sgettys]

Confirmed on Mac

[schristoff]

Thank you for your first contribution :D