Changes

fix(pingcap/tidb): remove pull_check_next_gen presubmit job configuration (#3672)

## Why

The `integrationtest` make task running inside the `check_next_gen` job
seems unnecessary (running tests/integrationtest/run-tests.sh), as it is
covered by `pull_integration_realcluster_test_next-gen`.
 (commit: 2aff745)