refactor(operator, yaml): remove unused disk CRD

[akhilerm]

Why is this PR required? What issue does it fix?:
Cleaning up of unused controller code

What this PR does?:
This PR removes unused disk CRD related code (installation and controller) and the related YAMLs.
On fresh installations:

• Disk CRD will not be installed

Existing installations:

• Existing disk resources will not be reconciled.

Does this PR require any upgrade changes?:
No

If the changes in this PR are manually verified, list down the scenarios covered::
Updated the v0.4.9 NDM operator and daemonset to an image using the changes. Everything worked fine.

Any additional information for your reviewer? :
Mention if this PR is part of any design or a continuation of previous PRs

Checklist:

• Fixes #
• PR Title follows the convention of <type>(<scope>): <subject>
• Has the change log section been updated?
• Commit has unit tests
• Commit has integration tests
• (Optional) Are upgrade changes included in this PR? If not, mention the issue/PR to track:
• (Optional) If documentation changes are required, which issue on https://github.com/openebs/openebs-docs is used to track them:

[codecov-io]

Codecov Report

Merging #412 into master will increase coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #412      +/-   ##
==========================================
+ Coverage   46.95%   47.14%   +0.19%     
==========================================
  Files          60       59       -1     
  Lines        2707     2683      -24     
==========================================
- Hits         1271     1265       -6     
+ Misses       1338     1322      -16     
+ Partials       98       96       -2     

Impacted Files	Coverage Δ
cmd/ndm_daemonset/controller/controller.go	18.36% <ø> (ø)
...md/ndm_daemonset/controller/sparsefilegenerator.go	87.95% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0dbc76c...ef57eda. Read the comment docs.