revert(autoware.repos): revert "feat: add ament_cmake fork (#370)" (#3054)

This reverts commit 0d06dd3.

Author: kenji-miyake

Diff for: autoware.repos

@@ -20,10 +20,6 @@ repositories:
     type: git
     url: https://github.com/tier4/autoware_auto_msgs.git
     version: tier4/main
-  core/external/ament_cmake:
-    type: git
-    url: https://github.com/autowarefoundation/ament_cmake.git
-    version: autoware-humble
   # universe
   universe/autoware.universe:
     type: git