Don't send message about DMing ACL when command's called from DM (#4188)

* Only send a message telling the user the file will be send via DM if the original message didn't come from a DM

* Remove unused import for AsyncIter

* Changed channel instance comparison to discord.DMChannel

Co-authored-by: douglas-cpp <douglasc.dev@gmail.com>

redbot/cogs/permissions/permissions.py

@@ -282,7 +282,8 @@ class Permissions(commands.Cog):
         except discord.Forbidden:
             await ctx.send(_("I'm not allowed to DM you."))
         else:
-            await ctx.send(_("I've just sent the file to you via DM."))
+            if not isinstance(ctx.channel, discord.DMChannel):
+                await ctx.send(_("I've just sent the file to you via DM."))
         finally:
             file.close()