[REVIEW] Fix duplicate cudatoolkit pinning issue

[galipremsagar]

This PR fixes a duplicate cudatoolkit pinning issue we are seeing in cudf packages:

This leads to following conda error:

Encountered problems while solving:
  - package cudf-22.08.00a220606-cuda_11_py39_g4d7595fb3f_113 requires cudatoolkit >=11.5,<12, but none of the providers can be installed

This PR also removes CC & CXX invocations, since we have switched to conda compilers: rapidsai/gpuci-build-environment#265

[bdice]

LGTM.

[galipremsagar]

@jakirkham | @ajschmidt8 any idea about the conda build we are seeing currently?: https://gpuci.gpuopenanalytics.com/job/rapidsai/job/gpuci/job/cudf/job/prb/job/cudf-cpu-python-build/CUDA=11.5,PYTHON=3.8/8562/console

[vyasr]

I think the error was from having the ignore_run_exports_from in the requirements section. I don't believe it's supported there, only in the build section. It looks like you've already fixed this though.

[galipremsagar]

rerun tests

[codecov]

Codecov Report

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[galipremsagar]

@gpucibot merge