RFR: 7903081: Update asmtools and remove jcov traces

[Christian Stein]

_work in progress..._

Blocked by AsmTools requiring JDK 17 (or above) to be built: https://github.com/openjdk/asmtools/blob/7ea57726a181b819c4b6331b19160c4fce238b11/build/build.properties#L30-L31

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Commit messages:
 - Update to use asmtools 8.1
 - 7903081: Update asmtools and remove jcov traces

Changes: https://git.openjdk.org/jtreg/pull/228/files
  Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=228&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903081
  Stats: 14 lines in 3 files changed: 0 ins; 7 del; 7 mod
  Patch: https://git.openjdk.org/jtreg/pull/228.diff
  Fetch: git fetch https://git.openjdk.org/jtreg.git pull/228/head:pull/228

PR: https://git.openjdk.org/jtreg/pull/228