Remove duplicates in `krel release-notes` output

[wilsonehusin]

What happened:

• Having headers in krel release-notes output caused the end result of k/k changelog to have duplicated headers. We had to fix this in 1.20 and again in 1.21 after the release.
• We also have duplicated dependencies section. In 1.21 we handled it in the same PR linked previously, while in 1.20 it was caught later on.

What you expected to happen:

Release notes team need not to manually edit document in k/sig-release before the release

How to reproduce it (as minimally and precisely as possible):

Create a minor release in k/k 😅

Anything else we need to know?:

/assign
/cc pmmalinov01 puerco

Environment:

• Cloud provider or hardware configuration: -
• OS (e.g: cat /etc/os-release): -
• Kernel (e.g. uname -a): -
• Others: -

[wilsonehusin]

/priority backlog

heh /cc doesn't work on issues, so manually now -- cc: @pmmalinov01 @puerco

[wilsonehusin]

/milestone 1.21

[k8s-ci-robot]

@wilsonehusin: The provided milestone is not valid for this repository. Milestones in this repository: [next, v1.16, v1.17, v1.18, v1.19, v1.20, v1.21, v1.22]

Use /milestone clear to clear the milestone.

In response to this:

/milestone 1.21

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[wilsonehusin]

/milestone v1.22

[jihoon-seo]

The code that generates the unwanted # Release notes for part:

release/pkg/notes/document/template.go

Lines 25 to 27 in c0d0213

	# Release notes for {{$CurrentRevision}}
	[Documentation](https://docs.k8s.io/docs/home)

---

The code that generates the unwanted # Changelog since (H1) part:

release/pkg/notes/document/template.go

Line 64 in c0d0213

# Changelog since {{$PreviousRevision}}

(c.f. The codes that generate the desired ## Changelog since (H2) part:)

• pkg/changelog/const.go
• pkg/notes/document/document.go

[jihoon-seo]

Note: This comment is Work In Progress.

[Call chains of appending-dependencies-changes functions]

• Call chain 1
  • ...
  • In cmd/krel/cmd/release_notes.go,
    func createDraftPR calls buildNotesResult(start, releaseNotes).
  • In cmd/krel/cmd/release_notes.go,
    func buildNotesResult() calls notes.NewDependencies().Changes().
• Call chain 2
  • ...
  • In pkg/changelog/changelog.go,
    func (c *Changelog) Run() calls c.impl.DependencyChanges(startRev, endRev).
• Call chain 3
  • ...
  • In cmd/release-notes/main.go,
    func run(*cobra.Command, []string) calls WriteReleaseNotes(releaseNotes).
  • In cmd/release-notes/main.go,
    func WriteReleaseNotes() calls notes.NewDependencies().ChangesForURL().