[jdk11u-dev] RFR: 8281507: Two javac tests have bad jtreg `@clean` tags

[Aleksey Shipilev]

Semi-clean backport on the way to jtreg update. Both files still have source/target=6 blocks, which need to be handled as well.

Additional testing:
 - [x] Affected tests now pass with new jtreg

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Commit messages:
 - Backport 86723d4892485651bcae735ed13545ea89b9bb22

Changes: https://git.openjdk.org/jdk11u-dev/pull/2556/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2556&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8281507
  Stats: 8 lines in 2 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2556.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2556/head:pull/2556

PR: https://git.openjdk.org/jdk11u-dev/pull/2556