Deprecate "Secondary Ownership" semantics

[thejcannon]

Currently only 3 targets have "secondary owners" fields:

• pex_binary
• python_awslambda (this assumes the filename is .py Doh!)
• python_google_cloud_function (this assumes the filename is .py Doh!)

The secondary ownership ability stems from wanting to use a goal by referring to the file (which presumably the "primary" owner doesn't support the goal). E.g. packageing a Python file packages the relevant PEX/Lambda/etc....

However, it is a bit short-sighted:

• You can run both a pex_binary (secondary) and a python_source (primary). If multiple PEX binaries exist for a single source:
  • Goals like run and paths error on ambiguity and give unhelpful messages (saying that the filename was ambiguous, and then listing the filename as a valid address)
• There are no secondary owners outside of Python.

So marking for deprecation and removal. Users can find the owners of the files from the specs and pipe that into the relevant goal. (If someone wants, we can add a new goal/flag to aid with this)

[kaos]

lgtm

[stuhood]

Nice! Thanks.

[Eric-Arellano]

Making python_source runnable was a fantastic idea. I agree that thanks to that, secondary ownership is not pulling its weight anymore.