Remove hardcoded xcode version

Bazel should work with the latest Xcode version (15.2) installed on CI.

PiperOrigin-RevId: 612803779
Change-Id: Ic2769068d17022fff53737afbfc93c14d3585fc1
diff --git a/.bazelci/postsubmit.yml b/.bazelci/postsubmit.yml
index 7346a35..059f392 100644
--- a/.bazelci/postsubmit.yml
+++ b/.bazelci/postsubmit.yml
@@ -211,7 +211,6 @@
       - build
       - test
   macos_arm64:
-    xcode_version: "15.1"
     shell_commands:
       - sed -i.bak -e 's/^# android_sdk_repository/android_sdk_repository/' -e 's/^#
         android_ndk_repository/android_ndk_repository/' WORKSPACE.bzlmod
diff --git a/.bazelci/presubmit.yml b/.bazelci/presubmit.yml
index bc6d62f..8591db3 100644
--- a/.bazelci/presubmit.yml
+++ b/.bazelci/presubmit.yml
@@ -269,7 +269,6 @@
       - test
   macos_arm64:
     shards: 2
-    xcode_version: "15.1"
     shell_commands:
       - sed -i.bak -e 's/^# android_sdk_repository/android_sdk_repository/' -e 's/^#
         android_ndk_repository/android_ndk_repository/' WORKSPACE.bzlmod