Twenty Fifteen: Don't escape translated strings.

Replace every unnecessary instance of `esc_html__()` and `esc_html_e()` with just `__()` and `_e()`.

Merges [30896] to the 4.1 branch.

see #30724.

Built from https://develop.svn.wordpress.org/branches/4.1@30924


git-svn-id: http://core.svn.wordpress.org/branches/4.1@30913 1a063a9b-81f0-0310-95a4-ce76da25c4cd