Clean up build.sh (pytorch#375)

* Re-enable hybrid_frontend tutorials

* clean up

Author: yf225

.jenkins/build.sh

@@ -53,7 +53,6 @@ popd
 
 # We will fix the hybrid frontend tutorials when the API is stable
 rm beginner_source/hybrid_frontend/learning_hybrid_frontend_through_example_tutorial.py || true
-rm beginner_source/hybrid_frontend/introduction_to_hybrid_frontend_tutorial.py || true
 
 aws configure set default.s3.multipart_threshold 5120MB