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; }
-    }
-    }