Twenty Fifteen: removing unused styles.

Props iamtakashi, fixes #30578.


Built from https://develop.svn.wordpress.org/trunk@30728


git-svn-id: http://core.svn.wordpress.org/trunk@30718 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: It's about time we call it one point oh.

Closes #30502.


Built from https://develop.svn.wordpress.org/trunk@30729


git-svn-id: http://core.svn.wordpress.org/trunk@30719 1a063a9b-81f0-0310-95a4-ce76da25c4cd