Core Metadata: Remove line suggesting metadata produces should use outdated versions

[CAM-Gerlach]

Presently, the Metadata-Version section of the core metadata spec states:

For broader compatibility, build tools MAY choose to produce distribution metadata using the lowest metadata version that includes all of the needed fields.

Following discussion on PEP 685's thread and related conversations on metadata-version, it seemed prudent to simply remove this; per @pfmoore

I would prefer to drop the quoted statement, and let the whole thing come under the “be strict in what you produce and lenient in what you consume” principle, so that metadata producers should always produce the latest version that they can, and consumers should be capable of dealing with older versions.

PEP 609 in turn delegates to the the PyPA Specifications document, which states:

All enhancements proposed this way must be discussed on the Packaging category of the Python.org Discourse prior to amending the PEP

I opened a thread on the packaging discourse to gather consensus and any objections to this change.