xenconfig: remove redunant parsing of device_model

device_model is parsed in xenParseOS(), then later in
xenParseConfigCommon().  <emulator> is not part of <os>,
so makes sense to remove the parsing in xenParseOS().

src/xenconfig/xen_common.c

@@ -1029,9 +1029,6 @@ xenParseOS(virConfPtr conf, virDomainDefPtr def)
 {
     size_t i;
 
-    if (xenConfigCopyStringOpt(conf, "device_model", &def->emulator) < 0)
-        return -1;
-
     if (STREQ(def->os.type, "hvm")) {
         const char *boot;