RFR: 8258192: Obsolete the CriticalJNINatives flag [v2]

[Coleen Phillimore]

> This change removes the disabled CriticalJNINatives code, and the flag now gives an obsolete message.
> Tested with tier1 on cpus x64, aarch64, and builds on linux-x86-open,linux-s390x-open,linux-arm32-debug,linux-ppc64le-debug.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Some platform adjustments.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6343/files
  - new: https://git.openjdk.java.net/jdk/pull/6343/files/7e9c641d..9b8ff9ae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6343&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6343&range=00-01

  Stats: 67 lines in 6 files changed: 0 ins; 57 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6343.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6343/head:pull/6343

PR: https://git.openjdk.java.net/jdk/pull/6343