Remove "must" language in unlinkability section.

index.html

@@ -3059,7 +3059,7 @@ <h3>Unlinkability</h3>
 payload is trustworthy for a given interaction. This characteristic is called
 <dfn class="lint-ignore">unlinkability</dfn> which ensures that no correlatable
 data are used in a digitally-signed payload while still providing some level of
-trust, the sufficiency of which must be determined by each verifier.
+trust, the sufficiency of which has to be determined by each verifier.
         </p>
 
         <p>