remove unused package

[bobzhang]

cc @Young-Flash any idea why this was not caught by the CI?

[coveralls]

Pull Request Test Coverage Report for Build 5306

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 87.902%

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Totals
Change from base Build 5300:	0.0%
Covered Lines:	5580
Relevant Lines:	6348

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💛 - Coveralls

[Yu-zh]

The package is used by the native backend but not other backends. moon should collect the warnings from moonc and when the unused package warning applies to all the backends, the warning should be reported to the user.