Revert "Disable rules_apple"

This reverts commit f71a3ff60e6e4706062a8e77e020afedbdc8e55a.
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index bc82239..e58a726 100644
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -108,11 +108,10 @@
         "git_repository": "https://github.com/bazelbuild/rules_appengine.git",
         "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_appengine/master/.bazelci/presubmit.yml"
     },
-    # TODO(https://github.com/bazelbuild/rules_apple/issues/243): reenable once fixed
-    # "rules_apple": {
-    #    "git_repository": "https://github.com/bazelbuild/rules_apple.git",
-    #    "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_apple/master/.bazelci/presubmit.yml"
-    #},
+    "rules_apple": {
+        "git_repository": "https://github.com/bazelbuild/rules_apple.git",
+        "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_apple/master/.bazelci/presubmit.yml"
+    },
     "rules_closure": {
         "git_repository": "https://github.com/bazelbuild/rules_closure.git",
         "http_config": "https://raw.githubusercontent.com/bazelbuild/rules_closure/master/.bazelci/presubmit.yml"