bip134: Remove wrong License header

The Copyright section specifies additional conditions, so the License
header is not correct (or at least misleading). So let's just remove it.
This is pragmatic because the field was only added as part of the
activation of BIP 2 anyway, and there are other old BIPs with a License
header.

bip-0134.mediawiki

@@ -6,7 +6,6 @@
   Status: Closed
   Type: Specification
   Assigned: 2016-07-27
-  License: CC-BY-SA-4.0 OR OPL
 </pre>
 
 ==Abstract==