copy-content: delete destination dirs before copying

[joelanford]

Description of the change:
Update the copy-content binary to always delete the destination directories to ensure they contain no extraneous content

Motivation for the change:
If a catalog pod using extractContent mode is restarted after the underlying catalog image changes (e.g. if a cluster is shutdown and the catalog is updated in the meantime), the copy-content init container re-runs and does not clear out the existing contents of the emptyDir, which causes the opm serve container to fail due to a mismatched digest.

Architectural changes:

Testing remarks:

Reviewer Checklist

• Implementation matches the proposed design, or proposal is updated to match implementation
• Sufficient unit test coverage
• Sufficient end-to-end test coverage
• Bug fixes are accompanied by regression test(s)
• e2e tests and flake fixes are accompanied evidence of flake testing, e.g. executing the test 100(0) times
• tech debt/todo is accompanied by issue link(s) in comments in the surrounding code
• Tests are comprehensible, e.g. Ginkgo DSL is being used appropriately
• Docs updated or added to /doc
• Commit messages sensible and descriptive
• Tests marked as [FLAKE] are truly flaky and have an issue
• Code is properly formatted

[grokspawn]

/approve
/lgtm