Shorten every instance of "CHANNEL" to "C" and whisper too

To save a little space in messages, it's getting very cramped

Modules/DeathReporter.lua

@@ -94,7 +94,7 @@ function shared.DeathReporter.Init()
 
 			---@type Message
 			local msg = {
-				channel = "CHANNEL",
+				channel = "C",
 				data = Heimdall_Data.config.deathReporter.masterChannel,
 				message = string.format(shared.L.en.killed,
 					source,
@@ -121,7 +121,7 @@ function shared.DeathReporter.Init()
 			if Heimdall_Data.config.echoToRussian then
 				-- Russian message
 				local ruMsg = {
-					channel = "CHANNEL",
+					channel = "C",
 					data = Heimdall_Data.config.deathReporter.masterChannel .. "ru",
 					message = string.format(shared.L.ru.killed,
 						source,