fix(config): deprecate the report_as field for challenges

This was a bad idea when it was added and it is irresponsible to
continue to have it. It causes more UX problems than it fixes with
slight of hand.

Closes: #1310
Closes: #1307
Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/config/testdata/good/thresholds.yaml

@@ -18,7 +18,6 @@ thresholds:
     challenge:
       algorithm: metarefresh
       difficulty: 1
-      report_as: 1
   - name: moderate-suspicion
     expression:
       all:
@@ -28,11 +27,9 @@ thresholds:
     challenge:
       algorithm: fast
       difficulty: 2
-      report_as: 2
   - name: extreme-suspicion
     expression: weight >= 20
     action: CHALLENGE
     challenge:
       algorithm: fast
       difficulty: 4
-      report_as: 4