Twenty Fifteen: remove fonts as a style dependency.

Merges [30832] to the 4.1 branch.

Props obenland, SergeyBiryukov.
Fixes #30678.

Built from https://develop.svn.wordpress.org/branches/4.1@30881


git-svn-id: http://core.svn.wordpress.org/branches/4.1@30869 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: remove Genericons as a dependency from loading the main stylesheet.

Merges [30865] to the 4.1 branch.

Props iamtakashi
See #30532.

Built from https://develop.svn.wordpress.org/branches/4.1@30882


git-svn-id: http://core.svn.wordpress.org/branches/4.1@30870 1a063a9b-81f0-0310-95a4-ce76da25c4cd