[KYUUBI #2039] Remove LegacyFlinkOperationSuite

### _Why are the changes needed?_

Replaced by FlinkOperationSuite

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [x] [Run test](https://kyuubi.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request

Closes #2039 from pan3793/flink.

Closes #2039

f9fd667 [Cheng Pan] Remove LegacyFlinkOperationSuite

Authored-by: Cheng Pan <chengpan@apache.org>
Signed-off-by: Cheng Pan <chengpan@apache.org>