RFR: 8329471: Remove GTK2 [v4]

[Alexander Zvegintsev]

> GTK2 support for Swing/AWT was deprecated for removal in JDK 21. 
> 
> It's being removed because no platform that supports the JDK needs it.
> 
> Manual and automated testing is green.

Alexander Zvegintsev has updated the pull request incrementally with one additional commit since the last revision:

  more cleanup

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/20378/files
  - new: https://git.openjdk.org/jdk/pull/20378/files/8e925cdf..b7665a77

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20378&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20378&range=02-03

  Stats: 9 lines in 1 file changed: 0 ins; 9 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20378.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20378/head:pull/20378

PR: https://git.openjdk.org/jdk/pull/20378