Disable impeller cmake test until it is fixed (flutter/engine#54788)

This task is consistently failing (with 3 retries for every engine commit). There is an issue to fix the problem, but until that issue is addressed, the task is primarily wasting CI resources.

engine/src/flutter/.ci.yaml

@@ -515,14 +515,6 @@ targets:
       - os=Mac-13|Mac-14
       - cpu=x86
 
-  - name: Mac impeller-cmake-example
-    bringup: true
-    recipe: engine_v2/engine_v2
-    timeout: 60
-    properties:
-      cpu: arm64
-      config_name: mac_impeller_cmake_example
-
   - name: Windows windows_android_aot_engine
     recipe: engine_v2/engine_v2
     timeout: 120

engine/src/flutter/ci/builders/mac_impeller_cmake_example.json

@@ -1,29 +0,0 @@
-{
-    "builds": [
-        {
-            "cas_archive": false,
-            "name": "ci/impeller-cmake-example",
-            "description": "Builds the Impeller cmake example.",
-            "archives": [],
-            "drone_dimensions": [
-                "device_type=none",
-                "os=Mac-13|Mac-14",
-                "cpu=arm64"
-            ],
-            "gclient_variables": {
-                "download_android_deps": false,
-                "download_jdk": false,
-                "download_impeller_cmake_example": true
-            },
-            "gn": [
-               "--impeller-cmake-example",
-               "--xcode-symlinks"
-            ],
-            "ninja": {
-                "config": "impeller-cmake-example",
-                "targets": [
-                ]
-            }
-        }
-    ]
-}