undo: add event removal undo command

This was a trivial copy & past of the event-adding undo command
with a switch of the undo() and redo() actions.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

commands/command_event.h

@@ -70,6 +70,18 @@ private:
 	event *eventToRemove;		// for undo and redo
 };
 
+class RemoveEvent : public EventBase {
+public:
+	RemoveEvent(struct dive *d, int dcNr, struct event *ev);
+private:
+	bool workToBeDone() override;
+	void undoit() override;
+	void redoit() override;
+
+	OwningEventPtr eventToAdd;	// for undo
+	event *eventToRemove;		// for redo
+};
+
 } // namespace Command
 
 #endif // COMMAND_EVENT_H