RenderEmojiPlain(emoji.ReplaceAliases) should be called explicitly for
some contents, but not for everything.
Actually in modern days, in most cases it doesn't need such
"ReplaceAliases". So only keep it for issue/PR titles.
If anyone really needs to do ReplaceAliases for some contents, I will
propose a following fix.
(cherry picked from commit 10c7996b5a5c705964fc6cc9c1817eea1fc436ef)
Conflicts:
templates/base/head.tmpl
context
f92c3de965