We no longer need to include headers we don't use for sudo*.h files.

Previously we needed to include headers required by the various
sudo*h files.  Now those files are more self-sufficient and we
should only include headers needed by code in the various .c files.

plugins/sudoers/sudoers.c

@@ -47,9 +47,7 @@
 #include <pwd.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <signal.h>
 #include <grp.h>
-#include <time.h>
 #include <netdb.h>
 #ifdef HAVE_LOGIN_CAP_H
 # include <login_cap.h>