Remove user fetching from blocked command (#3242)

We already have all the information we need to mention a user (their
id) and fetching the information from discord will lead to rate
limiting and extremely poor performance on large block lists for
no gain.

cogs/modmail.py

@@ -1665,13 +1665,7 @@ async def blocked(self, ctx):
                     self.bot.blocked_users.pop(str(id_))
                     logger.debug("No longer blocked, user %s.", id_)
                     continue
-
-            try:
-                user = await self.bot.get_or_fetch_user(int(id_))
-            except discord.NotFound:
-                users.append((id_, reason))
-            else:
-                users.append((user.mention, reason))
+            users.append((f"<@{id_}>", reason))
 
         blocked_roles = list(self.bot.blocked_roles.items())
         for id_, reason in blocked_roles: