[Shared Tasks] Cleanup shared task request and remove (#2341)

Functionally nothing should change in this patch. This refactors a lot
of formatting and code duplication in requests and member removals.

The long SharedTaskMessage namespace and its constants were contributing
to a lot of formatting that was difficult to read. These were shortened
since they're not all shared task specific anyway (though they should
probably just be moved to string_ids.h with other eqstrs now)

Shared task requests were refactored a little to remove an unnecessary
function that filled potential members. The separate functions used for
/taskquit and /taskremove were also combined into a single function to
remove a member while preserving live message differences.

zone/client_packet.cpp

@@ -15420,7 +15420,7 @@ void Client::Handle_OP_SharedTaskAddPlayer(const EQApplicationPacket *app)
 
 	if (!GetTaskState()->HasActiveSharedTask()) {
 		// this message is generated client-side in newer clients
-		Message(Chat::System, SharedTaskMessage::GetEQStr(SharedTaskMessage::COULD_NOT_USE_COMMAND));
+		Message(Chat::System, TaskStr::Get(TaskStr::COULD_NOT_USE_COMMAND));
 	}
 	else {
 		// struct