Revert "requirements.txt: make sure that cpu version of PyTorch gets installed"

This reverts commit 800f97c. It
doesn't work, pip still pulls in the CUDA dependencies. A proper
solution has been implemented during image building.

Author: hahnjo

requirements.txt

@@ -43,6 +43,3 @@ mplhep
 nbconvert>=7.4.0
 pytest
 setuptools
-
-# Look for CPU-only versions of PyTorch to avoid pulling CUDA in the CI docker images.
--f https://download.pytorch.org/whl/cpu/torch_stable.html