RFR: 8372651: Remove unreachable code in sun.awt.geom.AreaOp::calculate

[wb-zjp846396]

JBS: https://bugs.openjdk.org/browse/JDK-8372651

Summary:
- Fix a constant-condition `if` statement in `AreaOp.java` line 160.
- Clean up dead code and clarify control flow.

Testing:
- No functional modification involved.

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

Commit messages:
 - src/java.desktop: Remove unused code

Changes: https://git.openjdk.org/jdk/pull/28528/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28528&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372651
  Stats: 8 lines in 1 file changed: 0 ins; 8 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28528.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28528/head:pull/28528

PR: https://git.openjdk.org/jdk/pull/28528