RFR: 5066842: PKCS8EncodedKeySpec needs getAlgorithm method

[Weijun Wang]

Since the algorithm is already encoded inside a PKCS #8 data block, it is not necessary to provide an algorithm when a `PKCS8EncodedKeySpec` object is created. The same for `X509EncodedKeySpec`.

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Commit messages:
 - api change

Changes: https://git.openjdk.org/jdk/pull/10131/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10131&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-5066842
  Stats: 26 lines in 3 files changed: 23 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10131.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10131/head:pull/10131

PR: https://git.openjdk.org/jdk/pull/10131