Drop conversion webhook and v1alpha1 code

[enxebre]

What this PR does / why we need it:
Aggressive removal to see what breaks.
/hold

Which issue(s) this PR fixes (optional, use fixes #<issue_number>(, fixes #<issue_number>, ...) format, where issue_number might be a GitHub issue, or a Jira story:
Fixes #

Checklist

• Subject and description added to both, commit and PR.
• Relevant issues have been referenced.
• This change includes docs.
• This change includes unit tests.

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: enxebre

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[openshift-ci]

@enxebre: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-ibmcloud-roks	47152fe	link	false	/test e2e-ibmcloud-roks
ci/prow/e2e-aws	47152fe	link	true	/test e2e-aws
ci/prow/e2e-ibmcloud-iks	47152fe	link	false	/test e2e-ibmcloud-iks

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[openshift-merge-robot]

PR needs rebase.

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