fix(challenge): Slow and Steady Challenge not verifying correctly (@AnnaBuchholz) (monkeytypegame#6319)

### Description

I changed the Slow and Steady authentication to check if
"liveSpeedStyle" is "off" rather than checking the if the legacy
"showLiveWpm" was "false". This allows people to actually get the Slow
and Steady challenge role automatically instead of getting a failure
error even when they had liveSpeedStyle off.

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Author: AnnaBuchholz

frontend/static/challenges/_list.json

@@ -143,7 +143,7 @@
         "exact": 60
       },
       "config": {
-        "showLiveWpm": false,
+        "liveSpeedStyle": "off",
         "paceCaret": "off"
       }
     }