Move smoke pre-release tests to kotlinx-io repo

Before releasing the library, a set of smoke tests is executed to ensure that all artifacts were successfully published in sonatype snapshot repo.
Currently, these tests are in a pretty bad shape, and, what's worse, are in my personal repo: https://github.com/fzhinkin/kotlinx-io-release-smoke-test.

These tests should be moved to the main kotlinx-io repo.