Revert "Support both providerConfig and providerSpec under machine CRD's"

[ingvagabund]

Reverts #155 and keeps only the providerSpec field.

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[enxebre]

before merging this, please make sure to update https://github.com/openshift/console/search?q=providerConfig&unscoped_q=providerConfig

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ci/prow/e2e-aws	b9cdadd	link	/test e2e-aws
ci/prow/e2e-aws-operator	b9cdadd	link	/test e2e-aws-operator
ci/prow/images	b9cdadd	link	/test images

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