Re-enable the leak detection in MTRTestCase, now that the test leaks are fixed. (#33277)

diff --git a/src/darwin/Framework/CHIPTests/MTRPerControllerStorageTests.m b/src/darwin/Framework/CHIPTests/MTRPerControllerStorageTests.m
index 19f114f..06968b0 100644
--- a/src/darwin/Framework/CHIPTests/MTRPerControllerStorageTests.m
+++ b/src/darwin/Framework/CHIPTests/MTRPerControllerStorageTests.m
@@ -187,6 +187,10 @@
 
 - (void)setUp
 {
+    // Set detectLeaks true first, in case our superclass wants to do something
+    // in setUp when it's set.
+    self.detectLeaks = YES;
+
     // Per-test setup, runs before each test.
     [super setUp];
     [self setContinueAfterFailure:NO];
@@ -353,8 +357,6 @@
 
 - (void)test001_BasicControllerStartup
 {
-    self.detectLeaks = YES;
-
     __auto_type * factory = [MTRDeviceControllerFactory sharedInstance];
     XCTAssertNotNil(factory);
 
@@ -403,8 +405,6 @@
 
 - (void)test002_TryStartingTwoControllersWithSameNodeID
 {
-    self.detectLeaks = YES;
-
     __auto_type * rootKeys = [[MTRTestKeys alloc] init];
     XCTAssertNotNil(rootKeys);
 
diff --git a/src/darwin/Framework/CHIPTests/TestHelpers/MTRTestCase.mm b/src/darwin/Framework/CHIPTests/TestHelpers/MTRTestCase.mm
index b4cf92b..1dd1fea 100644
--- a/src/darwin/Framework/CHIPTests/TestHelpers/MTRTestCase.mm
+++ b/src/darwin/Framework/CHIPTests/TestHelpers/MTRTestCase.mm
@@ -27,7 +27,6 @@
  */
 - (void)tearDown
 {
-#if 0
 #if defined(ENABLE_LEAK_DETECTION) && ENABLE_LEAK_DETECTION
     if (_detectLeaks) {
         int pid = getpid();
@@ -36,7 +35,6 @@
         XCTAssertEqual(ret, 0, "LEAKS DETECTED");
     }
 #endif
-#endif
 
     [super tearDown];
 }