all: drop unnecessary includes of <errno.h> and <string.h>

"nm-macros-interal.h" already includes <errno.h> and <string.h>.
No need to include it everywhere else too.

src/main-utils.c

@@ -22,7 +22,6 @@
 #include "nm-default.h"
 
 #include <stdio.h>
-#include <errno.h>
 #include <fcntl.h>
 #include <stdlib.h>
 #include <unistd.h>