Remove KNOWN_COMMANDS check

Each time new command gets introduced this will have to be extended.
Outsource this check to Thrift which will raise informative `Impala::Protocol::Beeswax::BeeswaxException` instead

E.g.:

```
"Impala::Protocol::Beeswax::BeeswaxException", "AnalysisException: Syntax error in line 1:\nwat\n^\nEncountered: IDENTIFIER\nExpected: ALTER, COMPUTE, CREATE, DESCRIBE, DROP, EXPLAIN, INSERT, INVALIDATE, LOAD, REFRESH, SELECT, SHOW, USE, VALUES, WITH\n\nCAUSED BY: Exception: Syntax error"
```