RFR: 8284930: Re-examine FilterInputStream mark/reset

[Brian Burkhalter]

Remove the `synchronized` keyword from the `mark(int)` and `reset()` methods of `java.io.FilterInputStream`.

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Commit messages:
 - 8284930: Re-examine FilterInputStream mark/reset

Changes: https://git.openjdk.java.net/jdk/pull/8309/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8309&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284930
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8309.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8309/head:pull/8309

PR: https://git.openjdk.java.net/jdk/pull/8309