Tests: remove unnecessary import
Tests: remove unnecessary import

`SPMLibc.sleep` should be replaced with `Thread.Sleep(for:)`.  However,
there is no use of this in the test.  Simply remove the unnecessary
import.

abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager