Rename SystemDriver to WindowDriver and removed LinuxSystemDriver

Hopefully the last time I change my mind on what I want these to be
called. Reason behind this change is to minimize scope of a single
module. The WindowDriver should really only handle stuff related to
windows. If we need OS level functionality (e.g. get_os_name), that
should be the responsibility of the OS driver (or whatever that ends
being called). Remember, composition over inheritance.

engine/include/nova/platform/system.h

@@ -7,13 +7,13 @@
 #pragma once
 
 #include <nova/api.h>
-#include <nova/platform/system_driver.h>
+#include <nova/platform/window_driver.h>
 
 namespace Nova {
 	class NOVA_API System {
 	  public:
 		static void init();
 		static void shutdown();
-		static SystemDriver* get_driver();
+		static WindowDriver* get_driver();
 	};
 } // namespace Nova

engine/include/nova/platform/window_driver.h

@@ -9,9 +9,9 @@
 #include <nova/api.h>
 
 namespace Nova {
-	class NOVA_API SystemDriver {
+	class NOVA_API WindowDriver {
 	  public:
-		virtual ~SystemDriver() = default;
+		virtual ~WindowDriver() = default;
 
 		[[nodiscard]] virtual const char* get_surface_extension() const = 0;
 	};