RFR: No point in cleaning a bare materialization

[Robin Westberg]

We can skip the cleaning step when reusing a bare materialization.

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Commit messages:
 - No point in cleaning a bare materialization

Changes: https://git.openjdk.java.net/skara/pull/909/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=909&range=00
  Stats: 36 lines in 2 files changed: 35 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/909.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/909/head:pull/909

PR: https://git.openjdk.java.net/skara/pull/909