Remove deprecated GuildChannel methods

Remove the deprecated GuildChannel methods in preparation of an
incoming commit modifying GuildChannel.

Remove the following deprecated methods:

- `get_invites`
- `get_message`
- `get_messages`
- `get_reaction_users`
- `get_webhooks`

src/model/channel/guild_channel.rs

@@ -614,57 +614,6 @@ impl GuildChannel {
     pub fn webhooks(&self) -> Result<Vec<Webhook>> {
         self.id.webhooks()
     }
-
-    /// Alias of [`invites`].
-    ///
-    /// [`invites`]: #method.invites
-    #[deprecated(since="0.1.5", note="Use `invites` instead.")]
-    #[inline]
-    pub fn get_invites(&self) -> Result<Vec<RichInvite>> {
-        self.invites()
-    }
-
-    /// Alias of [`message`].
-    ///
-    /// [`message`]: #method.message
-    #[deprecated(since="0.1.5", note="Use `message` instead.")]
-    #[inline]
-    pub fn get_message<M: Into<MessageId>>(&self, message_id: M) -> Result<Message> {
-        self.message(message_id)
-    }
-
-    /// Alias of [`messages`].
-    ///
-    /// [`messages`]: #method.messages
-    #[deprecated(since="0.1.5", note="Use `messages` instead.")]
-    #[inline]
-    pub fn get_messages<F>(&self, f: F) -> Result<Vec<Message>>
-        where F: FnOnce(GetMessages) -> GetMessages {
-        self.messages(f)
-    }
-
-    /// Alias of [`reaction_users`].
-    ///
-    /// [`reaction_users`]: #method.reaction_users
-    #[deprecated(since="0.1.5", note="Use `reaction_users` instead.")]
-    #[inline]
-    pub fn get_reaction_users<M, R, U>(&self,
-                                       message_id: M,
-                                       reaction_type: R,
-                                       limit: Option<u8>,
-                                       after: Option<U>)
-        -> Result<Vec<User>> where M: Into<MessageId>, R: Into<ReactionType>, U: Into<UserId> {
-        self.reaction_users(message_id, reaction_type, limit, after)
-    }
-
-    /// Alias of [`webhooks`].
-    ///
-    /// [`webhooks`]: #method.webhooks
-    #[deprecated(since="0.1.5", note="Use `webhooks` instead.")]
-    #[inline]
-    pub fn get_webhooks(&self) -> Result<Vec<Webhook>> {
-        self.webhooks()
-    }
 }
 
 #[cfg(feature="model")]