different error-message structure in influxdb 1.8.x and 2.0.x when using InfluxQL

__Steps to reproduce:__

1. using influxdb 1.8.4, execute an invalid query using a POST request at `/query`, for example the query "SOMETHING"
2. the returned JSON will be like this:
```
{
"error": "error parsing query: found SOMETHING, expected SELECT, DELETE, SHOW, CREATE, DROP, EXPLAIN, GRANT, REVOKE, ALTER, SET,
KILL at line 1, char 1"
}
```
3. do the same with influxdb 2.0.4 (where the influxql-compatibility-things have been set up)
4. the returned JSON will be like this:
```
{
"code": "invalid",
"message": "failed to parse query: found SOMETHING, expected SELECT, DELETE, SHOW, CREATE, DROP, EXPLAIN, GRANT, REVOKE, ALTER,
SET, KILL at line 1, char 1"
}
```
5. the error-message structure is different between influxdb1 and influxdb2

__Expected behavior:__
Influx1 and Influx2 use the same error-message structure when queried in influxql-mode

__Actual behavior:__
Influx1 and Influx2 have different error-message structures when queried in influxql-mode

__Environment info:__

* System info: docker
* InfluxDB version: 1.8.4 and 2.0.4 in docker

__Config:__
default config used.

Reproduce the invalid InfluxQL request against the `/query` endpoint using the Docker-based InfluxDB 1.8.4 and 2.0.4 setups described in the issue, then trace the compatibility response handling. Done means both versions return the same error-message structure for equivalent InfluxQL parse failures, with regression coverage if the relevant test area is found.

Written by the indexing model from the issue text.