pcr: remove ccluster=main from connection strings

[dt]

Context: https://cockroachlabs.slack.com/archives/CHKQGKYEM/p1721138809661439

When a cluster is init'ed with --virtualized or --virtualized-empty, the main virtual cluster is the default so we don't need it in these connection strings. According to field teams, not all applications support it so removing it could reduce friction for those apps.

Jira issue: DOC-10685