RFR: 8367724: Remove Trailing Return Types from undecided list

[Kim Barrett]

Please review this trivial editorial change to the HotSpot Style Guide. This
change removes Trailing Return Types from the undecided list. This should have
been done as part of JDK-8366057, but was forgotten.

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Commit messages:
 - remove trailing return types from undecided list

Changes: https://git.openjdk.org/jdk/pull/27305/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27305&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367724
  Stats: 5 lines in 2 files changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27305.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27305/head:pull/27305

PR: https://git.openjdk.org/jdk/pull/27305