qemu: Fix double free of returned JSON array in qemuAgentGetVCPUs()

A part of the returned monitor response was freed twice and caused
crashes of the daemon when using guest agent cpu count retrieval.

 # virsh vcpucount dom --guest

Introduced in v1.0.6-48-gc6afcb0

src/qemu/qemu_agent.c

@@ -1529,7 +1529,6 @@ qemuAgentGetVCPUs(qemuAgentPtr mon,
 cleanup:
     virJSONValueFree(cmd);
     virJSONValueFree(reply);
-    virJSONValueFree(data);
     return ret;
 }