Swift: remove ModifiedStubMarkedAsGeneratedError

Author: redsun82

swift/actions/setup-env/action.yml

@@ -21,3 +21,4 @@ runs:
       shell: bash
       run: |
         echo build --repository_cache=~/.cache/bazel-repository-cache --disk_cache=~/.cache/bazel-disk-cache > ~/.bazelrc
+        echo test --test_output=errors

swift/codegen/generators/qlgen.py

@@ -43,10 +43,6 @@ class FormatError(Error):
     pass
 
 
-class ModifiedStubMarkedAsGeneratedError(Error):
-    pass
-
-
 class RootElementHasChildren(Error):
     pass