RFR: 8279066: Still see private key entries without certificates in a PKCS12 keystore

[Weijun Wang]

Before password-less PKCS12 keystores are supported, certificates in a PKCS12 file are always encrypted. Therefore if one loads the keystore with a null pass, it contains `PrivateKeyEntry`s without certificates. This has always been awkward (and most likely useless) so when JDK-8076190 introduced the password-less feature I also added a line to remove such an entry. 

https://github.com/openjdk/jdk/blob/a729a70c0119ed071ff490b0dfd4e3e2cb1a5ae4/src/java.base/share/classes/sun/security/pkcs12/PKCS12KeyStore.java#L2272 

Unfortunately, the line is not coded correctly, it should have been `remove(key)` but here it's `remove(value)`.

This code change correctly removes the entry.

That said, this behavior, although weird, has been there from the beginning since PKCS12 keystore was introduced. If you can find out a usage of a private key entry without any certificate and think it's worth kept that way, I can simply remove the `remove` call and leave the entry there.

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Commit messages:
 - 8279066: Still see private key entries without certificates in a PKCS12 keystore

Changes: https://git.openjdk.java.net/jdk/pull/6910/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6910&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279066
  Stats: 94 lines in 3 files changed: 87 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6910.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6910/head:pull/6910

PR: https://git.openjdk.java.net/jdk/pull/6910