test: record: remove file when it exists

We need to remove the file after the test, in particular because that's what make distcheck will expect, and it will error out if the file is left at the test location.

However, the current design of the recording feature doesn't guarantee that the file will exist as soon as the recording event is signaled, or even that it will even exist after the media player and libvlc instance are released, if no track data has been pushed to the pipeline.