Revert "Move the model property to the abstract repository"

This reverts commit 064cc099ec.

src/Repositories/MetricPoint/EloquentMetricPointRepository.php

@@ -7,6 +7,13 @@ use MetricPoint;
 
 class EloquentMetricPointRepository extends EloquentRepository implements MetricPointRepository
 {
+    /**
+     * The eloquent model instance.
+     *
+     * @var \MetricPoint
+     */
+    protected $model;
+
     /**
      * Create a new eloquent metric point repository instance.
      *