fix(progress-bar): removed duplicate label

[nikkimk]

Description

Removes duplicate label from progress bar.

Related issue(s)

• fixes #4225

How has this been tested?

• [ ] Test case 1
  1. Go here
  2. Right click the first progress bar example and choose Inspect Element
  3. From the Element Inspector click on the progress bar HTML and select Edit HTML
  4. Replace the existing progress bar HTML the following HTML: <sp-progress-bar label="" size="m" indeterminate ></sp-progress-bar>.
  5. Click Enter.
  6. Verify that the new progress bar displayed has no label.
  7. Right click the new progress bar's HTML and choose Add Attribute.
  8. Type the attribute label="label1".
  9. Click Enter.
  10. Verify that the progress bar label displays as label1 not label1label1.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)

Checklist

• [x] I have signed the Adobe Open Source CLA.
• [x] My code follows the code style of this project.
• [ ] If my change required a change to the documentation, I have updated the documentation in this pull request.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes. (Note: Testing won't allow an empty an empty label, so I can't test for this.)
• [x] All new and existing tests passed.
• [x] I have reviewed at the Accessibility Practices for this feature, see: Aria Practices