Remove pytest installation from CI script (added to docker image)

7 jobs for dev in 13 minutes and 9 seconds (queued for 8 minutes and 12 seconds)
Status Name Job ID Coverage
  Build
passed distcheck-build-linux-clang6-debug #38490

00:04:12

passed distcheck-build-linux-clang6-release #38489

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passed distcheck-build-linux-clang7-release #38491

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passed distcheck-build-linux-gcc7-debug #38486

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passed distcheck-build-linux-gcc7-release #38485

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passed distcheck-build-linux-gcc8-debug #38488

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passed distcheck-build-linux-gcc8-release #38487

00:05:29