chore: unused dep es6-promise

[yoshi-taka]

What does this PR do?

Remove es6-promise package.

This repogitory used the es6-promise package until around this commit: https://github.com/DataDog/datadog-api-client-typescript/commit/bbb0a5ef91d737307058f3928f24a81ee5b4d93b Although it’s not clear if this exact commit removed it, es6-promise is no longer used in the current v1 and v2.

Additional Notes

Review checklist

Please check relevant items below:

• [ ] This PR includes all newly recorded cassettes for any modified tests.

• [x] This PR does not rely on API client schema changes.

  • [x] The CI should be fully passing.

• [ ] Or, this PR relies on API schema changes and this is a Draft PR to include tests for that new functionality.

  • Note: CI shouldn't be run on this Draft PR, as its expected to fail without the corresponding schema changes.

[github-actions[bot]]

This PR has been automatically marked as stale because it has not had activity in the last 30 days. If there is no activity for another 90 days, this issue will be automatically closed.