nit: remove redundant CreateGuildRoleParams

CreateGuildRoleParams is identical to ModifyGuildRoleParams, so just use
the latter when creating new roles.

src/Discord.Net.Rest/API/Rest/CreateGuildRoleParams.cs

@@ -1,19 +0,0 @@
-using Newtonsoft.Json;
-
-namespace Discord.API.Rest
-{
-    [JsonObject(MemberSerialization = MemberSerialization.OptIn)]
-    public class CreateGuildRoleParams
-    {
-        [JsonProperty("name")]
-        public Optional<string> Name { get; set; }
-        [JsonProperty("permissions")]
-        public Optional<ulong> Permissions { get; set; }
-        [JsonProperty("color")]
-        public Optional<uint> Color { get; set; }
-        [JsonProperty("hoist")]
-        public Optional<bool> Hoist { get; set; }
-        [JsonProperty("mentionable")]
-        public Optional<bool> Mentionable { get; set; }
-    }
-    }

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -1174,7 +1174,7 @@ namespace Discord.API
             var ids = new BucketIds(guildId: guildId);
             return await SendAsync<IReadOnlyCollection<Role>>("GET", () => $"guilds/{guildId}/roles", ids, options: options).ConfigureAwait(false);
         }
-        public async Task<Role> CreateGuildRoleAsync(ulong guildId, Rest.CreateGuildRoleParams args, RequestOptions options = null)
+        public async Task<Role> CreateGuildRoleAsync(ulong guildId, Rest.ModifyGuildRoleParams args, RequestOptions options = null)
         {
             Preconditions.NotEqual(guildId, 0, nameof(guildId));
             options = RequestOptions.CreateOrClone(options);

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

@@ -264,7 +264,7 @@ namespace Discord.Rest
         {
             if (name == null) throw new ArgumentNullException(paramName: nameof(name));
 
-            var createGuildRoleParams = new API.Rest.CreateGuildRoleParams
+            var createGuildRoleParams = new API.Rest.ModifyGuildRoleParams
             {
                 Color = color?.RawValue ?? Optional.Create<uint>(),
                 Hoist = isHoisted,