Finalizing Terrain automated test conversions to utilize prefab system (#7360)

Signed-off-by: jckand-amzn <82226555+jckand-amzn@users.noreply.github.com>

AutomatedTesting/Gem/PythonTests/Terrain/TestSuite_Main.py

@@ -3,25 +3,18 @@ Copyright (c) Contributors to the Open 3D Engine Project.
 For complete copyright and license terms please see the LICENSE at the root of this distribution.
 
 SPDX-License-Identifier: Apache-2.0 OR MIT
-
 """
 
-# This suite consists of all test cases that are passing and have been verified.
-
 import pytest
-import os
-import sys
 
-from ly_test_tools import LAUNCHERS
 from ly_test_tools.o3de.editor_test import EditorTestSuite, EditorSharedTest
 
+
 @pytest.mark.SUITE_main
 @pytest.mark.parametrize("launcher_platform", ['windows_editor'])
 @pytest.mark.parametrize("project", ["AutomatedTesting"])
 class TestAutomation(EditorTestSuite):
 
-    enable_prefab_system = False
-
     class test_AxisAlignedBoxShape_ConfigurationWorks(EditorSharedTest):
         from .EditorScripts import TerrainPhysicsCollider_ChangesSizeWithAxisAlignedBoxShapeChanges as test_module