Simplify CronTrigger methods list & its usage

[MAILPOET-2538]

lib/AdminPages/Pages/Settings.php

@@ -76,7 +76,7 @@ class Settings {
     $data = [
       'settings' => $settings,
       'segments' => Segment::getSegmentsWithSubscriberCount(),
-      'cron_trigger' => CronTrigger::getAvailableMethods(),
+      'cron_trigger' => CronTrigger::METHODS,
       'total_subscribers' => Subscriber::getTotalSubscribers(),
       'premium_plugin_active' => License::getLicense(),
       'premium_key_valid' => !empty($premium_key_valid),

lib/Analytics/Reporter.php

@@ -30,7 +30,7 @@ class Reporter {
     global $wpdb, $wp_version, $woocommerce;
     $mta = $this->settings->get('mta', []);
     $newsletters = Newsletter::getAnalytics();
-    $isCronTriggerMethodWP = $this->settings->get('cron_trigger.method') === CronTrigger::$available_methods['wordpress'];
+    $isCronTriggerMethodWP = $this->settings->get('cron_trigger.method') === CronTrigger::METHOD_WORDPRESS;
     $checker = new ServicesChecker();
     $bounceAddress = $this->settings->get('bounce.address');
     $segments = Segment::getAnalytics();

lib/Cron/CronTrigger.php

@@ -12,12 +12,13 @@ class CronTrigger {
   const METHOD_MAILPOET = 'MailPoet';
   const METHOD_WORDPRESS = 'WordPress';
 
-  public static $available_methods = [
+  const METHODS = [
     'mailpoet' => self::METHOD_MAILPOET,
     'wordpress' => self::METHOD_WORDPRESS,
     'linux_cron' => self::METHOD_LINUX_CRON,
     'none' => 'Disabled',
   ];
+
   const DEFAULT_METHOD = 'WordPress';
   const SETTING_NAME = 'cron_trigger';
 
@@ -36,8 +37,4 @@ class CronTrigger {
       // cron exceptions should not prevent the rest of the site from loading
     }
   }
-
-  static function getAvailableMethods() {
-    return self::$available_methods;
-  }
 }

lib/Cron/DaemonHttpRunner.php

@@ -109,8 +109,7 @@ class DaemonHttpRunner {
   }
 
   function isCronTriggerMethodWordPress() {
-    $available_methods = CronTrigger::getAvailableMethods();
+    return $this->settings->get(CronTrigger::SETTING_NAME . '.method') === CronTrigger::METHOD_WORDPRESS;
-    return $this->settings->get(CronTrigger::SETTING_NAME . '.method') === $available_methods['wordpress'];
   }
 
   function checkWPTriggerExecutionRequirements() {

tests/integration/Cron/CronTriggerTest.php

@@ -34,11 +34,6 @@ class CronTriggerTest extends \MailPoetTest {
     );
   }
 
-  function testItCanReturnAvailableMethods() {
-    expect($this->cron_trigger->getAvailableMethods())
-      ->equals(CronTrigger::$available_methods);
-  }
-
   function testItCanInitializeCronTriggerMethod() {
     $settings_mock = Stub::makeEmpty(
       SettingsController::class,