lib: remove redundant and incorrect sys/fcntl.h include

POSIX defines <fcntl.h>, <sys/fcntl.h> is the same thing. However,
it should not be used as it's existence can depend on C-library
implementation. E.g. musl gives warning if <sys/fcntl.h> is used.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/lib/zebra.h b/lib/zebra.h
index 780e12e..3715b34 100644
--- a/lib/zebra.h
+++ b/lib/zebra.h
@@ -51,7 +51,6 @@
 #ifdef HAVE_STROPTS_H
 #include <stropts.h>
 #endif /* HAVE_STROPTS_H */
-#include <sys/fcntl.h>
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #endif /* HAVE_SYS_SELECT_H */