RFR: 8337229: Missing @Overrides in GlassSystemMenuShim

[Andy Goryachev]

Added missing @Overrides

We need to turn this warning into error in the gradle build.

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

Commit messages:
 - 8337229: Missing @Overrides in GlassSystemMenuShim

Changes: https://git.openjdk.org/jfx/pull/1517/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1517&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337229
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1517.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1517/head:pull/1517

PR: https://git.openjdk.org/jfx/pull/1517