RFR: 8259317: Remove JVM option BreakAtWarning

[Harold Seigel]

Please review this trivial change to remove the old JVM develop BreakAtWarning flag.

The change was tested with Mach5 tiers 1-3 on Linux, Windows, and Mac OS.

Thanks, Harold

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Commit messages:
 - 8259317: Remove JVM option BreakAtWarning

Changes: https://git.openjdk.java.net/jdk/pull/1966/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1966&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8259317
  Stats: 5 lines in 2 files changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1966.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1966/head:pull/1966

PR: https://git.openjdk.java.net/jdk/pull/1966