Remove "extends IHostedService" from classes where it's not required (#236)

Originally, these classes were services because I thought that all
DI-resolvable classes need to be services. However, this is not true, so
we can make these classes (notably Utility and GuildDataService) not
extend anything. `UtilityService` was renamed to `Utility` for
simplicity

---------

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

src/Commands/BanCommandGroup.cs

@@ -33,12 +33,12 @@ public class BanCommandGroup : CommandGroup
     private readonly IDiscordRestGuildAPI _guildApi;
     private readonly GuildDataService _guildData;
     private readonly IDiscordRestUserAPI _userApi;
-    private readonly UtilityService _utility;
+    private readonly Utility _utility;
 
     public BanCommandGroup(
         ICommandContext context, IDiscordRestChannelAPI channelApi, GuildDataService guildData,
         IFeedbackService feedback, IDiscordRestGuildAPI guildApi, IDiscordRestUserAPI userApi,
-        UtilityService utility)
+        Utility utility)
     {
         _context = context;
         _channelApi = channelApi;