RFR: 8282374: Java_sun_awt_X11_XlibWrapper_XSynchronize is wrong and unused

[Alexander Zvegintsev]

This fix simply removes unused `XSynchronize` method.

Alternatively its return type may be changed to `long`, but I think less code is better.

Testing is green.

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Commit messages:
 - remove XSynchronize

Changes: https://git.openjdk.java.net/jdk/pull/8016/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8016&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282374
  Stats: 13 lines in 2 files changed: 0 ins; 12 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8016.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8016/head:pull/8016

PR: https://git.openjdk.java.net/jdk/pull/8016