moveFile on windows forgot to delete src file in fallback case

moveFile on windows forgot to delete src file in fallback case

This dates back to commit 625303226dc94c2f35a5a4835b7c53c582014643,
where a cross-device moveFile on Windows was made to fall back to copying
to the destination, but forgot to delete the source file.

Should fix the following test suite failure on Windows:

    import:                                FAIL (2.52s)
      .\Test\Framework.hs:383:
      C:\Users\RUNNER~1\AppData\Local\Temp\importtest.0\import1\f exists unexpectedly
      Use -p '/import/' to rerun this test only.

Which was seen here, running the test suite in the github action environment.
https://github.com/psychoinformatics-de/git-annex-wheel/issues/5