Remove QueryRequest from GreptimeRequest

[MichaelScofield]

What type of enhancement is this?

Refactor

What does the enhancement do?

We have the QueryRequest in GreptimeRequest:

message GreptimeRequest {
  RequestHeader header = 1;
  oneof request {
    InsertRequests inserts = 2;
    QueryRequest query = 3; <-- here
    DdlRequest ddl = 4;
    DeleteRequests deletes = 5;
    RowInsertRequests row_inserts = 6;
    RowDeleteRequests row_deletes = 7;
  }
}

However, now the GreptimeRequest is not supposed to be used for query. So the QueryRequest in it (but not the QueryRequest itself!) can be deleted, along with some codes.

Implementation challenges

No response

[tisonkun]

IIUC we should remove the definition in https://github.com/GreptimeTeam/greptime-proto first?

[MichaelScofield]

@tisonkun right, but normally we first make the changes to proto at our own fork, then change the db codes, and finally merge the proto.

[tisonkun]

I found same of the dependencies to QueryRequest is from our inner client Database, that is related to #3798.

So this issue can be blocked from #3798.