[jdk11u-dev] RFR: 8206440: Remove javac -source/-target 6 from jdk regression tests

[Amos Shi]

Backport of [JDK-8206440](https://bugs.openjdk.org/browse/JDK-8206440)

Testing
- Local: Test passed on `MacOS 14.6.1` on Apple M1 Max
  - `OldenCompilingWithDefaults.java`: Test results: passed: 1
- Pipeline: 
- Testing Machine:

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

Commit messages:
 - Backport d2de786263e01b2036609621268853b14a1f46c3

Changes: https://git.openjdk.org/jdk11u-dev/pull/2915/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2915&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8206440
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2915.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2915/head:pull/2915

PR: https://git.openjdk.org/jdk11u-dev/pull/2915