RFR: 8278263: Remove redundant synchronized from URLStreamHandler.openConnection methods

[Andrey Turbanov]

All this Handler's are stateless and there is nothing to protect via synchronization.

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Commit messages:
 - [PATCH] Remove redundant synchronized from URLStreamHandler.openConnection methods

Changes: https://git.openjdk.java.net/jdk/pull/6373/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6373&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278263
  Stats: 36 lines in 3 files changed: 0 ins; 26 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6373.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6373/head:pull/6373

PR: https://git.openjdk.java.net/jdk/pull/6373