[VL] Remove useless ctx variable

[gaoyangxiaozhu]

What changes were proposed in this pull request?

Fix cpp compile warning isssue due to unused variable definitation 'ctx'

(Fixes: #ISSUE-ID)

How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)

(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

[github-actions]

Thanks for opening a pull request!

Could you open an issue for this pull request on Github Issues?

https://github.com/apache/incubator-gluten/issues

Then could you also rename commit message and pull request title in the following format?

[GLUTEN-${ISSUES_ID}][COMPONENT]feat/fix: ${detailed message}

See also:

• Other pull requests

[gaoyangxiaozhu]

@PHILO-HE / @rui-mo / @zhztheplayer

[PHILO-HE]

Thanks!