trim unrequired dirs and files from skipped list in boilerplate.py

Author: bharathbrat

hack/boilerplate/boilerplate.py

@@ -168,14 +168,10 @@ def file_extension(filename):
     'third_party',
     'vendor',
     '.venv',
-    
-    # These files are generated by an external generator.
-    'conformance/echo-basic/grpcechoserver',
-]
+    ]
 
 # list all the files contain 'DO NOT EDIT', but are not generated
-skipped_ungenerated_files = [
-    'hack/lib/swagger.sh', 'hack/boilerplate/boilerplate.py']
+skipped_ungenerated_files = ['hack/boilerplate/boilerplate.py']
 
 
 def normalize_files(files):