CBG-3855: Sequence range removal support

[gregns1]

CBG-3855

• Addition of support for removal of a given sequence range from the skipped sequence slice
• Note: RemoveSequences function this is hooked up to doesn't actually get called yet, this will be properly hooked up to cache with the work in CBG-3850

Pre-review checklist

• [ ] Removed debug logging (fmt.Print, log.Print, ...)
• [ ] Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• [ ] Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• [ ] GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/000/