Remove the default system prompt in the Llama 2 chat example (#1441) #2391

Job	Run time
build-and-test-cpp-x86_64 (ubuntu-20.04, mkl)	7m 6s
build-and-test-cpp-x86_64 (ubuntu-20.04, mkl)	7m 6s
build-and-test-cpp-x86_64 (ubuntu-20.04, dnnl)	7m 15s
build-and-test-cpp-x86_64 (ubuntu-20.04, dnnl)	7m 15s
build-and-test-cpp-x86_64 (macos-11, mkl)	10m 48s
build-and-test-cpp-x86_64 (macos-11, mkl)	10m 48s
build-and-test-cpp-x86_64 (macos-11, dnnl)	9m 45s
build-and-test-cpp-x86_64 (macos-11, dnnl)	9m 45s
check-python-style	14s
check-python-style	14s
build-and-push-docker-images	5m 31s
build-and-push-docker-images	5m 37s
build-and-test-cpp-aarch64 (openblas)	1m 15s
build-and-test-cpp-aarch64 (openblas)	44s
build-python-wheels (ubuntu-20.04, auto64)	4m 5s
build-python-wheels (ubuntu-20.04, auto64)	4m 20s
build-python-wheels (macos-11, auto64)	3m 45s
build-python-wheels (macos-11, auto64)	4m 0s
build-python-wheels (windows-2019, auto64)	4m 12s
build-python-wheels (windows-2019, auto64)	4m 23s
build-python-wheels (ubuntu-20.04, aarch64)	7m 58s
build-python-wheels (ubuntu-20.04, aarch64)	4m 20s
build-python-wheels (macos-11, arm64)	6m 46s
build-python-wheels (macos-11, arm64)	4m 18s
build-and-deploy-docs	0s
build-and-deploy-docs	0s
test-python-wheels	0s
test-python-wheels	0s
publish-python-wheels-on-pypi	0s
publish-python-wheels-on-pypi	0s
	2h 11m 30s

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