revert defaulter-gen

[theishshah]

Description of the change:
Revert defaulter-gen changes made in #1050

Motivation for the change:
Discussion on #1038

[hasbro17]

Can you reformat the commit message according to our guidelines.

Also add a line in the removed section of the CHANGELOG to point this out. And probably mention that defaulting for CRs should be done with mutating webhooks.

[joelanford]

Should we also remove defaulter-gen references from internal/pkg/scaffold/gopkgtoml.go and sdk-cli-reference.md?

[hasbro17]

@joelanford Yes good catch.
@theishshah Can you update the PR to remove the constraint for defaulter-gen from the scaffold:
https://github.com/operator-framework/operator-sdk/blob/master/internal/pkg/scaffold/gopkgtoml.go#L46
And update the example in the CLI reference as well:
https://github.com/operator-framework/operator-sdk/blob/master/doc/sdk-cli-reference.md#example-1

[hasbro17]

You need to update gopkgtoml_test.go to remove "k8s.io/code-generator/cmd/defaulter-gen" from the required imports as well.

[joelanford]

@theishshah I'm confused why some of these 0.7.0 changes are showing up in this PR. I checked master to be sure and all of them are already there. Maybe some weirdness happened with merging or rebasing after 0.7.0 was released?

[estroz]

Yeah you might want to squash merge onto master.

[joelanford]

LGTM. Just one nit.