Jenkinsfile: enable 'Cockroach Backwards Compatibility' tests

We had an issue with CRDB where newer version forbid type
of SQL query we were using. We disabled CRDB bc tests until we
will have release without problematic query. Now we can enable
tests.

Change-Id: I275cbecebdcbfef587281f2daaf677d01860b23d

Jenkinsfile.public

@@ -308,12 +308,6 @@ pipeline {
                 }
 
                 stage('Cockroach Backwards Compatibility') {
-                    // skip this stage until next release because of
-                    // https://www.cockroachlabs.com/docs/releases/v21.2.html#v21-2-3-sql-language-changes
-                    when {
-                        expression { false }
-                    }
-
                     environment {
                         STORJ_NETWORK_HOST4 = '127.0.0.5'
                         STORJ_NETWORK_HOST6 = '127.0.0.5'