Both the old and new pager summary are announced by screen reader when page changed

The pager summary has the aria-relevant=all. This tells the screen reader to announce both the removed and added text. Causing both to be announced, for example:

• Viewing page 1. Showing records 1 - 20 of 164 items.
• Viewing page 2. Showing records 21 - 40 of 164 items.

Which is rather confusing, as at first it seems that the page didn't change. Setting aria-relevant to "text" (default) or "additions" may perform better.

Steps to reproduce:

1. Open the Pager demo
2. With VoiceOver enabled click on a different page link
3. Noice that the the old page summary and new page summary are both announced.