RFR: JDK-8257237: Cleanup unused imports in the SunJSSE provider implementation

[Xue-Lei Andrew Fan]

This change cleanups the unused imports in the SunJSSE provider implementation.  Cleanup only, no new regression test.

Bug: https://bugs.openjdk.java.net/browse/JDK-8257237

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Commit messages:
 - cleanup unused imports in the SunJSSE provider implementation

Changes: https://git.openjdk.java.net/jdk/pull/1508/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1508&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8257237
  Stats: 6 lines in 3 files changed: 0 ins; 5 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1508.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1508/head:pull/1508

PR: https://git.openjdk.java.net/jdk/pull/1508