Remove version from package.json

[swissspidy]

This is similar to #1328 / #1333.

The version field (and actually name too) in package.json is optional if you don't plan to publish your package.

Given that private is set to true in package.json to prevent accidental publication, there's no harm in omitting the version field.

This makes the release process a bit easier and less prone to mistakes when changing the version everywhere.