Remove redundant Pagination header

Problem/Motivation

The "Pagination" nav elements are labelled both by a hidden header and an aria-label attribute. They should only have one and since it is hidden, it would be best for it to be the attribute. Removing the header also fixes accessibility errors related to skipped heading levels or improper nesting of headers.

Proposed resolution

Remove the headers and the aria-labelledby attributes that refer to them.

Remaining tasks

Implement.

User interface changes

None. (Currently, aria-label is ignored because aria-labelledby is present.)

API changes

None.

Data model changes

None.