RFR: 7903095: Use diamond operator in jtreg

[Christian Stein]

Update jtreg to use the diamond operator to eliminate reduct use of type arguments.

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Commit messages:
 - 7903095: Use diamond operator in jtreg

Changes: https://git.openjdk.java.net/jtreg/pull/52/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=52&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903095
  Stats: 77 lines in 24 files changed: 0 ins; 0 del; 77 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/52.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/52/head:pull/52

PR: https://git.openjdk.java.net/jtreg/pull/52