Update Language to be more user friendly when checking logs

CRM/Core/BAO/ActionSchedule.php

@@ -549,7 +549,7 @@ FROM civicrm_action_schedule cas
     // dev/core#369 If an SMS provider is deleted then the relevant row in the action_schedule_table is set to NULL
     // So we need to exclude them.
     if (CRM_Utils_System::isNull($schedule->sms_provider_id)) {
-      return ["sms_provider_missing" => "SMS Provider is NULL in database cannot send reminder"];
+      return ["sms_provider_missing" => "SMS reminder cannot be sent because the SMS provider has been deleted."];
     }
 
     $messageSubject = $tokenRow->render('subject');

tests/phpunit/api/v3/JobTest.php

@@ -412,7 +412,7 @@ class api_v3_JobTest extends CiviUnitTestCase {
     $this->assertEquals($sentToID, $theChosenOneID);
     $cronlog = CRM_Core_DAO::executeQuery("SELECT * FROM civicrm_action_log")->fetchAll()[0];
     $this->assertEquals(1, $cronlog['is_error']);
-    $this->assertEquals('SMS Provider is NULL in database cannot send reminder', $cronlog['message']);
+    $this->assertEquals('SMS reminder cannot be sent because the SMS provider has been deleted.', $cronlog['message']);
     $this->setupForSmsTests(TRUE);
   }