Remove unused 'target' field in virDomainHostdevDef

The virDomainHostdevDef struct contains a 'char *target'
field. This is set to 'NULL' when parsing XML and never
used / set anywhere else. Clearly it is bogus & unused

* src/conf/domain_conf.c, src/conf/domain_conf.h: Remove
  target from virDomainHostdevDef

src/conf/domain_conf.c

@@ -893,7 +893,6 @@ void virDomainHostdevDefFree(virDomainHostdevDefPtr def)
     if (!def)
         return;
 
-    VIR_FREE(def->target);
     virDomainDeviceInfoClear(&def->info);
     VIR_FREE(def);
 }
@@ -4774,7 +4773,6 @@ virDomainHostdevDefParseXML(const xmlNodePtr node,
         virReportOOMError();
         return NULL;
     }
-    def->target = NULL;
 
     mode = virXMLPropString(node, "mode");
     if (mode) {

src/conf/domain_conf.h

@@ -792,7 +792,6 @@ struct _virDomainHostdevDef {
             int dummy;
         } caps;
     } source;
-    char* target;
     int bootIndex;
     virDomainDeviceInfo info; /* Guest address */
 };