Revert "install cuda_python_test_helpers as editable"

This reverts commit baac405.

Author: rparolin

ci/tools/run-tests

@@ -70,12 +70,6 @@ elif [[ "${test_module}" == "core" ]]; then
     FREE_THREADING+="-ft"
   fi
 
-  # Install test helpers used by cuda_core tests
-  pushd ./cuda_python_test_helpers
-  echo "Installing cuda_python_test_helpers (editable)"
-  pip install -e .
-  popd
-
   pushd ./cuda_core
   if [[ "${LOCAL_CTK}" == 1 ]]; then
     # We already installed cuda-bindings, and all CTK components exist locally,