Fix error reporting in seqcli query

[nblumhardt]

> seqcli query -q "select count(*) from stream where a != b group by @Level"
The query could not be executed.

 - Syntax error (line 1, column 37): unsupported operator `!=`.                                                                                                                      
 - SQL queries only support `=`, `<>`, `and`, `or`, and `not` in logical expressions.                                                                                                
                                                                                                                                                                                     
Perhaps you meant:                                                                                                                                                                   
                                                                                                                                                                                     
select count(*) from stream where a <> b group by @Level

[nblumhardt]

Just spotted that I still need to remove the helper and update the MCP tool.

[KodrAus]

nit: Since WriteCell already accepts some context to tell whether it's a heading or not, it seems reasonable to fold the , separator in there too.

[nblumhardt]

Done, munched down to much less code