Move TRITON_CONSTRAINT setting to common binary_populate_env.sh, BE - Cleanup unused build scripts (#120744)
1. This moves TRITON_CONSTRAINT to common binary_populate_env.sh so that this is set for all wheels.
test in CI via ``ciflow/binaries`` label. Please note we only setting this constraint when PYTORCH_EXTRA_INSTALL_REQUIREMENTS is set. And this variable is set for all the wheels that gets uploaded to pypi. Hence triton wheels need to be set at the same place.
This is done for regular wheels and rocm wheels separately, since rocm wheels using different triton package
3. Cleanup legacy unused code
Test:
``
git grep setup_linux_system_environment.sh
``
Needs: https://github.com/pytorch/builder/pull/1712
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120744
Approved by: https://github.com/huydhn
