Refactor: migrate SortManifests and its test case to releaseutil

[lentil1016]

What this PR does / why we need it:

Hi. I'm currently working on a new feature on branch dev-v3 and I found a TODO in my way to implement this feature.

helm/pkg/action/install.go

Lines 293 to 299 in 86d8596

	// Sort hooks, manifests, and partials. Only hooks and manifests are returned,
	// as partials are not used after renderer.Render. Empty manifests are also
	// removed here.
	// TODO: Can we migrate SortManifests out of pkg/tiller?
	hooks, manifests, err := releaseutil.SortManifests(files, vs, releaseutil.InstallOrder)
	if err != nil {
	// By catching parse errors here, we can prevent bogus releases from going

• merge sortManifests and its test case in pkg/tiller into pkg/releaseutil
• merge Manifest, manifestFile, result in pkg/tiller into pkg/releaseutil
• replace the SortByKind in releaseutil
• remove trivial code in tiller package.

Special notes for your reviewer:

If applicable:

• this PR contains documentation
• this PR contains unit tests
• this PR has been tested for backwards compatibility

[lentil1016]

@adamreese OK, This PR was trying to refactor SortManifests in pkg/tiller package out. But it seems someone has done this refactor and being merged before me. Good job.
Luckily I don't need to close this PR, for he forgot to remove an expired TODO comment. 🤣