Remove bogus free of static strings

Remove bogus free of statically allocated strings introduced
in 03ca4204

* src/conf/capabilities.c: Don't free static strings for
  default disk driver type/name

src/conf/capabilities.c

@@ -175,9 +175,6 @@ virCapabilitiesFree(virCapsPtr caps) {
     VIR_FREE(caps->host.secModel.doi);
     virCPUDefFree(caps->host.cpu);
 
-    VIR_FREE(caps->defaultDiskDriverName);
-    VIR_FREE(caps->defaultDiskDriverType);
-
     VIR_FREE(caps);
 }