release-21.2: sql: dropping user with default privilege's error message is more clear

[cockroach-teamcity]

Exalate commented:

cockroachdb/cockroach#77142 --- Release note (sql change): When dropping a user that has default privileges, the error message now includes which database and schema the default privileges are defined in. Additionally a hint is given to show exactly how to remove the default privileges. Example: role testuser2 cannot be dropped because some objects depend on it owner of default privileges on new sequences belonging to role testuser2 in database testdb2 privileges for default privileges on new sequences belonging to role testuser3 in database testdb2 privileges for default privileges on new sequences for all roles in database test privileges for default privileges on new sequences for all roles in database testdb2

Jira Issue: DOC-2764

Jira Issue: DOC-4358