RFR: 8283340: Remove support for -Dsun.misc.URLClassPath.disableJarChecking

[Liam Miller-Cushon]

This change removes support for `-Dsun.misc.URLClassPath.disableJarChecking`. As discussed in the bug the feature doesn't current work, and only ever supported scenarios where a security manager is installed, so it seems safe to remove.

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Commit messages:
 - 8283340: Remove support for -Dsun.misc.URLClassPath.disableJarChecking

Changes: https://git.openjdk.java.net/jdk/pull/7861/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7861&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283340
  Stats: 25 lines in 1 file changed: 0 ins; 20 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7861.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7861/head:pull/7861

PR: https://git.openjdk.java.net/jdk/pull/7861