DEV: Remove JoyPixels emoji option (#12197)

- removes the option from site settings
- deletes the site setting on existing sites that have it
- marks posts using emojis as requiring a rebake

Note that the actual image files are not removed here, the plan is to
remove them in a few weeks/months (when presumably the rebaking of old
posts has been completed).

plugins/discourse-details/test/javascripts/lib/details-cooked-test.js.es6

@@ -5,7 +5,7 @@ module("lib:details-cooked-test");
 const defaultOpts = buildOptions({
   siteSettings: {
     enable_emoji: true,
-    emoji_set: "emoji_one",
+    emoji_set: "google_classic",
     highlighted_languages: "json|ruby|javascript",
     default_code_lang: "auto",
   },