Exclude self newspace from oldspace decomposition

[wwylele]

This partially fixes #6104 in the affected newspace pages (knowl still has the problem). I chose the approach to keep this as oldspace decomposition and remove the extra self newspace. I find it better to keep the semantics of this section, as it contrast with the previous section ("Decomposition of $S^{new}$" and "Decomposition of $S^{old}$")

[AndrewVSutherland]

@wwylele if you email me at [email protected] I can send you a token you can use to create an account that will let you make knowl edits, and also an invite to the LMFDB zulip.

[AndrewVSutherland]

I would also encourage you to add yourself to https://github.com/LMFDB/lmfdb/blob/main/CONTRIBUTORS.yaml (you can do that in this PR if you wish).

[wwylele]

Thanks! I added myself there

[wwylele]

I also submitted an edit to https://beta.lmfdb.org/knowledge/show/cmf.decomposition.old.gamma1. I kept the decomposition of the full space there because I find it less wordy

[AndrewVSutherland]

Sorry for the delay, I'm reviewing this now and expect to merge it shortly (@edgarcosta can you hold off pushing to dev until that happens? It looks like there are some test failures in any case).