WoW:API GuildControlDelRank
Deletes the rank at that index. The player must be the guild leader.
The index must be between 1 and the value returned by GuildControlGetNumRanks().
The index rank must be unused meaning that no guildmembers may currently have that rank or any lower rank (having a higher index value).
No return value. If the rank cannot be deleted, a message written be sent to the default chat window.