Kernel/Graphics: Don't assert when disabling TextModeConsole

Not sure how it's useful to do so, let's not assert if something tries
to disable it. If we will use TextModeConsole as a boot console, that
console will be disabled after loading an appropriate console to replace
it.

Kernel/Graphics/Console/TextModeConsole.h

@@ -31,7 +31,7 @@ public:
     virtual void flush(size_t, size_t, size_t, size_t) override { }
 
     virtual void enable() override { }
-    virtual void disable() override { VERIFY_NOT_REACHED(); }
+    virtual void disable() override { }
 
 private:
     void clear_vga_row(u16 row);