FIX: remove div used to measure textarea position

Also corrects the positioning of autocomplete (when typing @ or emoji)

Previously there were edge conditions where autocomplete would be hundreds
of pixels away due to a bug measuring.


This correct an issue where Firefox ends up having an enormous blank space
at the bottom of topics after editing.

app/assets/javascripts/discourse/lib/autocomplete.js.es6

@@ -285,11 +285,10 @@ export default function(options) {
       hOffset = 0;
     } else {
       pos = me.caretPosition({
-        pos: completeStart,
-        key: options.key
+        pos: completeStart + 1
       });
 
-      hOffset = 27;
+      hOffset = 10;
       if (options.treatAsTextarea) vOffset = -32;
     }