RFR: 8375561: Class NGGroup is in need of some cleanup [v4]

[Christopher Schnick]

> This should improve the code quality of the class while preserving its original workings

Christopher Schnick has updated the pull request incrementally with one additional commit since the last revision:

  Remove unused imports

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Changes:
  - all: https://git.openjdk.org/jfx/pull/2043/files
  - new: https://git.openjdk.org/jfx/pull/2043/files/d29fcc80..e5637626

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=2043&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=2043&range=02-03

  Stats: 5 lines in 1 file changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/2043.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2043/head:pull/2043

PR: https://git.openjdk.org/jfx/pull/2043