Remove queryMismatch, in favor of unrecognizedMessage.

The aggregator behavior on receiving this error is the same either way,
and there are many other message-based errors that do not get their own
code. This change effectively leaves it up to implementations to decide
the level of detail they include in error reports.

unrecognizedMessage might seem like a strange error to use since the
message is invalid, not unrecognized; however, this error is used for
all message-parsing errors, and may soon be renamed to invalidMessage
(in #464).

draft-ietf-ppm-dap.md

@@ -511,7 +511,6 @@ in the "type" field (within the DAP URN namespace
 | batchMismatch              | Aggregators disagree on the report shares that were aggregated in a batch. |
 | unauthorizedRequest        | Authentication of an HTTP request failed (see {{request-authentication}}). |
 | missingTaskID              | HPKE configuration was requested without specifying a task ID. |
-| queryMismatch              | Query type indicated by a message does not match the task's query type. |
 | roundMismatch              | The aggregators disagree on the current round of the VDAF preparation protocol. |
 | batchOverlap               | A request's query includes reports that were previously collected in a different batch. |
 
@@ -1268,7 +1267,7 @@ This message consists of:
       specify the batch window instead.]
 
   The indicated query type MUST match the task's query type. Otherwise, the
-  Helper MUST abort with error "queryMismatch".
+  Helper MUST abort with error "unrecognizedMessage".
 
   This field is called the "partial" batch selector because, depending on the
   query type, it may not determine a batch. In particular, if the query type is
@@ -1759,7 +1758,7 @@ struct {
 The named parameters are:
 
 * `query`, the Collector's query. The indicated query type MUST match the task's
-  query type. Otherwise, the Leader MUST abort with error "queryMismatch".
+  query type. Otherwise, the Leader MUST abort with error "unrecognizedMessage".
 * `agg_param`, an aggregation parameter for the VDAF being executed. This is the
   same value as in `AggregationJobInitReq` (see {{leader-init}}).
 
@@ -1892,7 +1891,7 @@ message contains the following parameters:
     * For fixed_size tasks, the request specifies the batch ID.
 
   The indicated query type MUST match the task's query type. Otherwise, the
-  Helper MUST abort with "queryMismatch".
+  Helper MUST abort with "unrecognizedMessage".
 
 * `agg_param`: The opaque aggregation parameter for the VDAF being executed.
   This value MUST match the AggregationJobInitReq message for each aggregation