Remove jazzy and Xcode properties from impeller-cmake-example builder (flutter/engine#41222)

This builder doesn't use or install jazzy or Xcode, remove the
properties from the config.

Passing without these properties:
https://ci.chromium.org/p/flutter/builders/try/Mac%20impeller-cmake-example/14

engine/src/flutter/.ci.yaml

@@ -460,12 +460,6 @@ targets:
       release_build: "true"
       cpu: arm64
       config_name: mac_impeller_cmake_example
-      $flutter/osx_sdk : >-
-        { "sdk_version": "14a5294e" }
-      dependencies: >-
-        [
-          {"dependency": "jazzy", "version": "0.14.1"}
-        ]
 
   - name: Windows Android AOT Engine
     recipe: engine/engine