RFR: 8280970: Cleanup dead code in java.security.Provider

[Andrey Turbanov]

Method `Provider.getKey` was added in [JDK-8276660](https://bugs.openjdk.java.net/browse/JDK-8276660). It was unused since introduction.
Method `EngineDescription.getConstructorParameterClass()` and field `EngineDescription.constructorParameterClass` is unused since [JDK-7191662](https://bugs.openjdk.java.net/browse/JDK-7191662)

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Commit messages:
 - [PATCH] Cleanup dead code in java.security.Provider

Changes: https://git.openjdk.java.net/jdk/pull/7164/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7164&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280970
  Stats: 14 lines in 1 file changed: 0 ins; 14 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7164.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7164/head:pull/7164

PR: https://git.openjdk.java.net/jdk/pull/7164