Fix generation of ConfigureWindow request

When parsing requests, the extension name of xproto is the empty string,
not the string "xproto".

When deleting the extraneous content from the ConfigureWindow request,
the third content becomes the second after the second has been deleted.
Therefore to remove contents at indices 2 and 3, we actually have to
remove from index 2 twice.
Regenerate xproto

Regenerate xproto with the fix for ConfigureWindow request.