RFR: 8301994: Remove unused code from awt_List.cpp

[Rajat Mahajan]

Remove commented out/ unused code from awt_List.cpp, which has been commented out since 2007, when the code was moved to Mercurial.
The test ScrollPaneLimitation.java has been opened under [JDK-8306137](https://bugs.openjdk.org/browse/JDK-8306137), and it should be safe to remove this code now.

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Commit messages:
 - Remove unused code from awt_List.cpp

Changes: https://git.openjdk.org/jdk/pull/17378/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17378&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301994
  Stats: 10 lines in 1 file changed: 0 ins; 10 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17378.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17378/head:pull/17378

PR: https://git.openjdk.org/jdk/pull/17378