bip-reconcil: Switch PD "license" to CC0

See https://github.com/bitcoin/bips/blob/master/bip-0002.mediawiki#recommended-licenses

bip-reconcil.mediawiki

@@ -8,7 +8,7 @@
   Status: Draft
   Type: Standards Track
   Created: 2010-00-00
-  License: PD
+  License: CC0-1.0
 </pre>
 
 ==Abstract==
@@ -293,4 +293,4 @@ We would like to thank Ben Woosley for contributions to the high-level descripti
 
 ==Copyright==
 
-This document is placed in the public domain.
+This document is licensed under the Creative Commons CC0 1.0 Universal license.