This function is strange. Looks like the implementation is of low quality.

```
bool isDeterministic() const override { return false; }
bool isDeterministicInScopeOfQuery() const override { return false; }
```
Why it is not deterministic? Missing a comment.

```
String convertToJson(const PODArray<String> & variant_names, const Variants & variants)
{
    FormatSettings settings;

    WriteBufferFromOwnString buf;

    writeCString("{\"data\":[", buf);
    for (size_t i = 0; i < variants.size(); ++i)
    {
        writeCString("{\"variant_name\":", buf);
        writeJSONString(variant_names[i], buf, settings);
        writeCString(",\"x\":", buf);
        writeText(variants[i].x, buf);
        writeCString(",\"y\":", buf);
        writeText(variants[i].y, buf);
        writeCString(",\"beats_control\":", buf);
        writeText(variants[i].beats_control, buf);
        writeCString(",\"to_be_best\":", buf);
        writeText(variants[i].best, buf);
        writeCString("}", buf);
        if (i != variant_names.size() -1)
            writeCString(",", buf);
    }
    writeCString("]}", buf);

    return buf.str();
}
```
It returns unstructured data? :scream: 

As first step we can remove documentation for this function.
CC @nikitamikhaylov 
void registerFunctionsGeo(FunctionFactory &);
void registerFunctionsIntrospection(FunctionFactory &);
void registerFunctionsNull(FunctionFactory &);
void registerFunctionsJSON(FunctionFactory &);
void registerFunctionsSQLJSON(FunctionFactory &);
void registerFunctionToJSONString(FunctionFactory &);
void registerFunctionsConsistentHashing(FunctionFactory & factory);
void registerFunctionsUnixTimestamp64(FunctionFactory & factory);
void registerFunctionBitHammingDistance(FunctionFactory & factory);
void registerFunctionTupleHammingDistance(FunctionFactory & factory);
void registerFunctionsStringHash(FunctionFactory & factory);
void registerFunctionValidateNestedArraySizes(FunctionFactory & factory);
void registerFunctionsSnowflake(FunctionFactory & factory);
#if !defined(ARCADIA_BUILD)
void registerFunctionBayesAB(FunctionFactory &);
#endif
void registerFunctionTid(FunctionFactory & factory);
void registerFunctionLogTrace(FunctionFactory & factory);
#if USE_SSL
void registerFunctionEncrypt(FunctionFactory & factory);
void registerFunctionDecrypt(FunctionFactory & factory);
void registerFunctionAESEncryptMysql(FunctionFactory & factory);
void registerFunctionAESDecryptMysql(FunctionFactory & factory);
#endif
void registerFunctions()
{
    auto & factory = FunctionFactory::instance();
    registerFunctionsArithmetic(factory);
    registerFunctionsArray(factory);
    registerFunctionsTuple(factory);