Remove now unused patch -- we have strndup(3).

No bump because because code was #ifndef HAVE_STRNDUP ... so it wasn't
picked up anymore.

devel/libmagic/patches/patch-src_softmagic_c

@@ -1,39 +0,0 @@
-$OpenBSD: patch-src_softmagic_c,v 1.4 2009/04/04 18:28:15 rui Exp $
---- src/softmagic.c.orig	Fri Nov  7 22:50:37 2008
-+++ src/softmagic.c	Sat Mar 28 13:22:45 2009
-@@ -331,21 +331,26 @@ check_fmt(struct magic_set *ms, struct magic *m)
- 
- #ifndef HAVE_STRNDUP
- char * strndup(const char *, size_t);
-+size_t strnlen (const char *, size_t);
- 
-+size_t
-+strnlen (const char *string, size_t maxlen)
-+{
-+  const char *end = memchr (string, '\0', maxlen);
-+  return end ? (size_t) (end - string) : maxlen;
-+}
-+
- char *
- strndup(const char *str, size_t n)
- {
--	size_t len;
--	char *copy;
-+	size_t len = strnlen (str, n);
-+	char *copy = malloc (len + 1);
- 
--	len = strlen(str);
--	if (len > n)
--		len = n;
--	if (!(copy = malloc(len + 1)))
--		return (NULL);
--	(void) memcpy(copy, str, len + 1);
-+	if (copy == NULL)
-+		return NULL;
-+
- 	copy[len] = '\0';
--	return (copy);
-+	return memcpy (copy, str, len); 
- }
- #endif /* HAVE_STRNDUP */
-