Fix implicit function declaration warnings

src/Platform.c

@@ -1,7 +1,8 @@
 #define _GNU_SOURCE
 
-#include "PlatformThreads.h"
 #include "Platform.h"
+#include "PlatformThreads.h"
+#include "PlatformSockets.h"
 
 #include <enet/enet.h>
 
@@ -9,9 +10,6 @@
 // in PltSleepMsInterruptible().
 #define INTERRUPT_PERIOD_MS 50
 
-int initializePlatformSockets(void);
-void cleanupPlatformSockets(void);
-
 struct thread_context {
     ThreadEntry entry;
     void* context;