<Swing Dev> RFR: 8263496: MetalHighContrastTheme.getControlHighlight cleanup

[Prasanta Sadhukhan]

SonarCloud reports the potential issue with MetalHighContrastTheme.getControlHighlight where `controlHighlight ` field is not used and the getControlHighlight() uses secondary field.
public ColorUIResource getControlHighlight() {
        // This was super.getSecondary3();
        return secondary2;
    } 
Removed the unused field.

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Commit messages:
 - 8263496: MetalHighContrastTheme.getControlHighlight cleanup

Changes: https://git.openjdk.java.net/jdk/pull/3149/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3149&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263496
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3149.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3149/head:pull/3149

PR: https://git.openjdk.java.net/jdk/pull/3149