xen: Fix domain dump

Remove redundant 'live' parameter which caused an error from xend:

    "xend.err 'Too many values for live'"

src/xen/xend_internal.c

@@ -3026,7 +3026,7 @@ xenDaemonDomainCoreDump(virDomainPtr domain, const char *filename,
     }
 
     return xend_op(domain->conn, domain->name,
-                   "op", "dump", "file", filename, "live", "0",
+                   "op", "dump", "file", filename,
                    "live", (flags & VIR_DUMP_LIVE ? "1" : "0"),
                    "crash", (flags & VIR_DUMP_CRASH ? "1" : "0"),
                    NULL);