Fixes diff line content getting cached on the frontend

Removes the memoize call for the diff line conent
which can sometimes result in incorrect diff line conent
being displayed when navigating by commit.

app/assets/javascripts/diffs/components/diff_row.vue

@@ -140,16 +140,13 @@ export default {
     },
     (line) => line.type,
   ),
-  lineContent: memoize(
-    (line) => {
+  lineContent: (line) => {
     if (line.isConflictMarker) {
       return line.type === CONFLICT_MARKER_THEIR ? 'HEAD//our changes' : 'origin//their changes';
     }
 
     return line.rich_text;
   },
-    (line) => line.line_code,
-  ),
   CONFLICT_MARKER,
   CONFLICT_MARKER_THEIR,
   CONFLICT_OUR,