Redundancy across metastore docs

I noticed that the [metastores](https://github.com/apache/polaris/blob/main/site/content/in-dev/unreleased/metastores.md) doc has a lot of the same information as the [Production Configuration](https://github.com/apache/polaris/blob/main/site/content/in-dev/unreleased/configuring-polaris-for-production.md) doc and wonder if we can just remove the metastores doc.

Most of it is about the deprecated eclipselink metastore, and as for JDBC it doesn't include much information beyond what's already in "Production Configuration". Also, confusingly, it doesn't tell you how to configure your metastore. It shows the env vars, but doesn't explicitly tell you they're env vars which need to be set:

Compare site/content/in-dev/unreleased/metastores.md with site/content/in-dev/unreleased/configuring-polaris-for-production.md, checking which information is duplicated or still needed. Review the deprecated EclipseLink and JDBC sections and the metastore environment-variable guidance. Done means the documentation has one clear, non-redundant source of truth and no needed configuration details are lost.

Written by the indexing model from the issue text.