[ci_yaml] Remove hard coding platform list

This allows ci.yamls to control what platforms are available

This was initially enforced during the migration to surface
errors. It is no longer needed as we move to a more ci.yaml
focussed system

Bug: None

Change-Id: I20b5f308651df3c7ad7bbe036e61dd0f7fe717cf
Reviewed-on: https://flutter-review.googlesource.com/c/infra/+/27540
Reviewed-by: Keyong Han <keyonghan@google.com>
Commit-Queue: Casey Hillers <chillers@google.com>
diff --git a/config/lib/ci_yaml/ci_yaml.star b/config/lib/ci_yaml/ci_yaml.star
index 4c6e020..868da27 100644
--- a/config/lib/ci_yaml/ci_yaml.star
+++ b/config/lib/ci_yaml/ci_yaml.star
@@ -371,11 +371,8 @@
 
 def _target_platform(target):
     """Return the target platform based on the name."""
-    supported_platforms = ("Linux", "Linux_android", "Mac", "Mac_android", "Mac_ios", "Mac_ios32", "Windows", "Windows_android")
     platform = target.name.split(" ")[0]
-    if platform in supported_platforms:
-        return platform.lower()
-    fail("Failed to find platform for %s" % target.name)
+    return platform.lower()
 
 def _generate(repo, branch, version, testing_ref, dimensions = {}, properties = {}, triggering_policy = None, notifies = None, recipes_ref = "refs/heads/main"):
     # CQ group configurations. Only FLUTTER_RECIPES is using