python: Don't generate bodies for close callback functions

Commit 6ed5a1b9 adds close callback
functions to the public API but doesn't add python implementation. This
patch sets the function to be written manually (to fix the build), but
doesn't implement them yet.

python/generator.py

@@ -425,6 +425,8 @@ skip_impl = (
     'virDomainGetInterfaceParameters',
     'virDomainGetCPUStats',
     'virDomainGetDiskErrors',
+    'virConnectUnregisterCloseCallback',
+    'virConnectRegisterCloseCallback',
 )
 
 qemu_skip_impl = (