[Improvement] Remove legacy version variables and related configuration options in v6

[asbjornu]

We currently have quite a few version variables and related configuration options that are tailored towards sytems that don't support SemVer 2.0, such as LegacySemVerPadding, BuildMetaDataPadding, CommitsSinceVersionSourcePadding, etc.

We should remove these in v6, at least from Core. If pepole still need these, we should look into adding them through an extension to the Core somehow.

[stale]

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