chore(GlSprintf): migrate stories to CSF

What does this MR do?

chore(GlSprintf): migrate stories to CSF

This also removes the storyshots for the component. This was done because:

• The component doesn't generate any of its own markup or text; its output is completely defined by the props/slots given to it.
• The unit specs for the component are much more thorough than the storyshots, and test a superset of what the storyshots test.

Addresses #1299 (closed).

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• [-] If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• [-] If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• [-] If the MR changes a component's API, integration MR(s) have been opened in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • [-] GitLab: mr_url
  • [-] CustomersDot: mr_url
  • [-] Status Page: mr_url
• [-] Added the ~"component:*" label(s) if applicable.

Closes #1299 (closed)