fix: :bug: Theme accordion styles conflict with Details block Fixes #252

[Herm71]

What does this do/fix?

See Issue #252. This fixes a conflict with the Details block by removing the enqueuing of accordion.css

QA

Links to relevant issues

• Issue #252

Tests

Does this have tests?

• [ ] Yes
• [x] No, this doesn't need tests because... Rob will review this PR and approve it!
• [ ] No, I need help figuring out how to write the tests.

[knice]

@Herm71 How does this affect existing sites and uses of the accordion block?

[knice]

We still need this stylesheet while the current accordion implementation is in place.