Revert "feat: add system monitor feature with panel toggle and event handling"

This reverts commit aee7030b30.

include/dwn.h

@@ -107,7 +107,6 @@ typedef struct Workspace Workspace;
 typedef struct Monitor Monitor;
 typedef struct Panel Panel;
 typedef struct Config Config;
-typedef struct SystemMonitor SystemMonitor;
 
 struct Client {
     Window window;
@@ -177,8 +176,6 @@ typedef struct {
     Panel *top_panel;
     Panel *bottom_panel;
 
-    SystemMonitor *sysmon;
-
     Config *config;
 
     bool running;