Kernel+LibC: Move errno definitions to Kernel/API/POSIX

This fixes at least half of our LibC includes in the kernel. The source
of truth for errno codes and their description strings now lives in
Kernel/API/POSIX/errno.h as an enumeration, which LibC includes.

Kernel/Net/Socket.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <AK/StringView.h>
+#include <Kernel/API/POSIX/errno.h>
 #include <Kernel/Debug.h>
 #include <Kernel/FileSystem/OpenFileDescription.h>
 #include <Kernel/Net/IPv4Socket.h>
@@ -13,7 +14,6 @@
 #include <Kernel/Net/Socket.h>
 #include <Kernel/Process.h>
 #include <Kernel/UnixTypes.h>
-#include <LibC/errno_numbers.h>
 
 namespace Kernel {