RFR: 8255536: Remove the directsign property and option

[Weijun Wang]

I regret adding the `directsign` property/option to JarSigner/jarsigner. See the bug for details.

-------------

Commit messages:
 - 8255536: Remove the directsign property and option

Changes: https://git.openjdk.java.net/jdk/pull/915/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=915&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255536
  Stats: 184 lines in 7 files changed: 14 ins; 162 del; 8 mod
  Patch: https://git.openjdk.java.net/jdk/pull/915.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/915/head:pull/915

PR: https://git.openjdk.java.net/jdk/pull/915