RFR: 8291957: Redundant import statements in sun.security.ec

[raspberry-hu]

remove unused imports

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Commit messages:
 - Update XDHPublicKeyImpl.java
 - Update SunEC.java
 - Update ECKeyPairGenerator.java

Changes: https://git.openjdk.org/jdk/pull/9792/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9792&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291957
  Stats: 9 lines in 3 files changed: 0 ins; 9 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9792.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9792/head:pull/9792

PR: https://git.openjdk.org/jdk/pull/9792