RFR: 8302806: (fs) Remove unused enum sun.nio.file.SensitivityWatchEventModifier

[Brian Burkhalter]

This enum is not used in the JDK and did not appear in external source code searches.

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Commit messages:
 - 8302806: (fs) Remove unused enum sun.nio.file.SensitivityWatchEventModifier

Changes: https://git.openjdk.org/jdk/pull/12626/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12626&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302806
  Stats: 65 lines in 1 file changed: 0 ins; 65 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12626.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12626/head:pull/12626

PR: https://git.openjdk.org/jdk/pull/12626