Revert "Extract setting up ec2 linux and checkout to be composite actions (#80462)"
This reverts commit fe8bfef8a66510a717b626918196a7e996cbd6be.
Reverted https://github.com/pytorch/pytorch/pull/80462 on behalf of https://github.com/malfet due to Broke binary builds, see https://hud.pytorch.org/pytorch/pytorch/commit/fe8bfef8a66510a717b626918196a7e996cbd6be
