virt-aa-helper: Drop unused variable in verify_xpath_context()

After one of previous commits (v5.10.0-524-gce56408e) there is
a variable left unused in verify_xpath_context() which breaks the
build.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/security/virt-aa-helper.c

@@ -541,7 +541,6 @@ valid_path(const char *path, const bool readonly)
 static int
 verify_xpath_context(xmlXPathContextPtr ctxt)
 {
-    int rc = -1;
     char *tmp = NULL;
 
     if (!ctxt) {