Decide on use of cmp for Secondary Literature and Institutions

[ahankinson]

Following on from #1689 , the role of "Composer" in these record types is also RISM-specific and should be clarified.

cmp for secondary lit typically means that the entry is about, or related, to a person as a composer, e.g., "The life and times of J.S. Bach" would get a cmp entry.

We're not entirely sure what the relator code of cmp for institutions means. It's possible that there is some conflation between old and new muscat. Perhaps @Docudoctor knows?

Probably these relator codes should be removed from these records. For secondary literature, asn or oth are possible, but we can also get in touch with the LoC to see if they are willing to create a new one for "topical name" or something like that.