Switch static var to using Civi::statics

This static variable is actually problematic. Moving it to statics will allow us to stop reseting it
in the test suite & to hone in on where it is actually broken rather than the test suite
is not flushing it

CRM/Member/BAO/Membership.php

@@ -1331,13 +1331,15 @@ public static function sortName($id) {
    */
   public static function createRelatedMemberships(&$params, &$dao, $reset = FALSE) {
     // CRM-4213 check for loops, using static variable to record contacts already processed.
-    static $relatedContactIds = [];
+    if (!isset(\Civi::$statics[__CLASS__]['related_contacts'])) {
+      \Civi::$statics[__CLASS__]['related_contacts'] = [];
+    }
     if ($reset) {
-      // We need a way to reset this static variable from the test suite.
-      // @todo consider replacing with Civi::$statics but note reset now used elsewhere: CRM-17723.
-      $relatedContactIds = [];
+      // CRM-17723.
+      unset(\Civi::$statics[__CLASS__]['related_contacts']);
       return FALSE;
     }
+    $relatedContactIds  = &\Civi::$statics[__CLASS__]['related_contacts'];
 
     $membership = new CRM_Member_DAO_Membership();
     $membership->id = $dao->id;

tests/phpunit/CiviTest/CiviUnitTestCase.php

@@ -1838,8 +1838,6 @@ public function quickCleanUpFinancialEntities() {
     $this->quickCleanup($tablesToTruncate);
     CRM_Core_DAO::executeQuery("DELETE FROM civicrm_membership_status WHERE name NOT IN('New', 'Current', 'Grace', 'Expired', 'Pending', 'Cancelled', 'Deceased')");
     $this->restoreDefaultPriceSetConfig();
-    $var = TRUE;
-    CRM_Member_BAO_Membership::createRelatedMemberships($var, $var, TRUE);
     $this->disableTaxAndInvoicing();
     $this->setCurrencySeparators(',');
     CRM_Core_PseudoConstant::flush('taxRates');