Twenty Fifteen: remove fonts as a style dependency.

Props obenland, SergeyBiryukov. Fixes #30678.

git-svn-id: https://develop.svn.wordpress.org/trunk@30832 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: update readme.txt file, props iamtakashi. See #30675.

git-svn-id: https://develop.svn.wordpress.org/trunk@30833 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: update archive pagination links to use `aria-hidden` for better accessibility.

Props SergeyBiryukov, fixes #30152.

git-svn-id: https://develop.svn.wordpress.org/trunk@30834 602fd350-edb4-49c9-b593-d223f7449a82