Deprecate noarch_python_build_age MetaData/Config setting

[kenodegard]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

Let's deprecate the unused noarch_python_build_age configuration value. It is not formally defined in either the old nor new recipe formats, isn't mentioned in our docs, and has no hits on GitHub or on Google.

It was introduced in 26dfe8e (in conda-build 3.21.0).

Why is this needed?

Remove tech-debt related to this block of code:

conda-build/conda_build/render.py

Lines 805 to 832 in 683ea91

	# don't bother distributing python if it's a noarch package, and figure out
	# which python version we prefer. `python_age` can use used to tweak which
	# python gets used here.
	if metadata.noarch or metadata.noarch_python:
	from .conda_interface import VersionOrder
	age = int(
	metadata.get_value(
	"build/noarch_python_build_age", metadata.config.noarch_python_build_age
	)
	)
	versions = []
	for variant in variants:
	if "python" in variant:
	vo = variant["python"]
	if vo not in versions:
	versions.append(vo)
	version_indices = sorted(
	range(len(versions)), key=lambda k: VersionOrder(versions[k].split(" ")[0])
	)
	if age < 0:
	age = 0
	elif age > len(versions) - 1:
	age = len(versions) - 1
	build_ver = versions[version_indices[len(versions) - 1 - age]]
	variants = filter_by_key_value(
	variants, "python", build_ver, "noarch_python_reduction"
	)

What should happen?

No response

Additional Context

No response