Fix strdup configure test: Remove a call to the undeclared free
function.
Submitted upstream: <https://github.com/networkupstools/nut/pull/1720>
diff --git a/configure.ac b/configure.ac
index 3aa26c24ebc99bb6..c93ccd1e494874d5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -294,7 +294,6 @@ AC_CACHE_CHECK([for strdup(s)],
char *t = "Test";
char *s = strdup(t);
if (!s || !(s[0]=='T'&&s[1]=='e'&&s[2]=='s'&&s[3]=='t'&&s[4]=='\0') || s == t) res = 1;
-if (s) free (s);
if (res != 0) return res
/* autoconf adds ";return 0;" */
]])],