[spec] Remove redundant 'is chaff' field (#1282)

spec.bs

@@ -2802,7 +2802,6 @@ a [=list=] of [=interest groups=] |bidIgs|, and a [=list=] of [=bid debug report
     Issue: TODO: Link deserialization to IETF standard when available.
     (<a href="https://github.com/WICG/turtledove/issues/1254">WICG/turtledove#1254</a>)
 1. If |response| is failure, then return failure.
-1. If |response|'s [=server auction response/is chaff=] is true, return failure.
 1. If |response|'s [=server auction response/top level seller=] is not null:
   1. If |topLevelAuctionConfig| is null return failure.
   1. If |topLevelAuctionConfig|'s [=auction config/seller=] is not equal to
@@ -3064,8 +3063,6 @@ A <dfn>server auction response</dfn> is a [=struct=] that contains auction resul
 from an auction executed on the trusted auction server. It has the following [=struct/items=]:
 
 <dl dfn-for="server auction response">
-  : <dfn>is chaff</dfn>
-  :: A [=boolean=] field indicating whether this response should be ignored.
   : <dfn>ad render url</dfn>
   :: [=URL=]. The [=leading bid info/leading bid=]'s [=generated bid/ad descriptor=]'s [=ad descriptor/url=] from the
      auction.