chore: remove deprecated fields in ExtensionJson

[netomi]

This PR removes two fields in the ExtensionJson response object that are deprecated for a long time:

• namespaceAccess
• unrelatedPublisher

The do not fit into the current model anymore and should not be used.

[Copilot]

Pull request overview

This PR removes two long-deprecated properties (namespaceAccess, unrelatedPublisher) from the server-side ExtensionJson API model and stops populating them in registry responses, aligning the JSON response shape with the current namespace/verification model.

Changes:

• Removed deprecated unrelatedPublisher and namespaceAccess fields (and their getters/setters) from ExtensionJson.
• Removed server-side population of those fields in LocalRegistryService and deleted the now-unused RESTRICTED_ACCESS constant.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
server/src/main/java/org/eclipse/openvsx/LocalRegistryService.java	Stops setting deprecated ExtensionJson fields and removes unused constant.
server/src/main/java/org/eclipse/openvsx/json/ExtensionJson.java	Removes deprecated fields and updates equals/hashCode accordingly.

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[netomi]

There are more deprecated fields, namely allVersions in ExtensionJson and SearchEntryJson. They are in active used and will need a different approach for actual removal.

[netomi]

Added some more cleanups to this PR that are harmless.