fix some typos & remove `using` added by VS

src/Discord.Net.Core/Entities/Guilds/IGuild.cs

@@ -1241,7 +1241,7 @@ namespace Discord
             RequestOptions options = null);
 
         /// <summary>
-        ///     Gets the welcome screen of the guild. Returns <see langword="null"/> is the welcome channel is not set.
+        ///     Gets the welcome screen of the guild. Returns <see langword="null"/> if the welcome channel is not set.
         /// </summary>
         /// <returns>
         ///     A task that represents the asynchronous creation operation. The task result contains a <see cref="WelcomeScreen"/>.

src/Discord.Net.Core/Entities/Guilds/WelcomeScreenChannel.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Xml.Linq;
 
 namespace Discord;
 

src/Discord.Net.Rest/Entities/Guilds/GuildHelper.cs

@@ -972,7 +972,7 @@ namespace Discord.Rest
         public static async Task<WelcomeScreen> ModifyWelcomeScreenAsync(bool enabled, string description, WelcomeScreenChannelProperties[] channels, IGuild guild, BaseDiscordClient client, RequestOptions options)
         {
             if (!guild.Features.HasFeature(GuildFeature.Community))
-                throw new InvalidOperationException("Cannot update welcome screed in a non-community guild.");
+                throw new InvalidOperationException("Cannot update welcome screen in a non-community guild.");
 
             var args = new ModifyGuildWelcomeScreenParams
             {