Revert "Remove deprecated ProviderReference methods"

[janwillies]

This reverts commit 2ba47acab1a23806a3ffa9cbd1cdf9a3ff80653e.

Signed-off-by: Jan Willies jan.willies@accenture.com

Description of your changes

Generated code is missing ProviderReference but until https://github.com/crossplane/crossplane-runtime/pull/241 is merged the Managed interface still references it, resulting in errors like this:

angryjet: error: error loading packages using pattern ./...: /Users/jan.willies/golang/src/github.com/crossplane-contrib/provider-gitlab/apis/projects/v1alpha1/zz_generated.managedlist.go:36:14: cannot use &l.Items[i] (value of type *Project) as resource.Managed value in assignment: missing method GetProviderReference

I have:

• [x] Read and followed Crossplane's [contribution process].
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

manual