compiler/test/unit/semantic/imports.d: call deinitializeDMD

[the-horo]

There is the unit/deinitialization.d test that checks that variables are empty before calling initDMD. If this test happens to be run right before that one then the latter will fail.

[dlang-bot]

Thanks for your pull request and interest in making D better, @the-horo! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
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• New or modified functions have Ddoc comments (with Params: and Returns:)

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