RFR: 8293984: Unnecessary Vector usage in PropertyEditorSupport

[Andrey Turbanov]

Field PropertyEditorSupport.listeners is accessed only under `synchronized(this)`.
It means extra synchronization by Vector is not needed.

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Commit messages:
 - [PATCH] Unnecessary Vector usage in PropertyEditorSupport

Changes: https://git.openjdk.org/jdk/pull/10331/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10331&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293984
  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/10331.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10331/head:pull/10331

PR: https://git.openjdk.org/jdk/pull/10331