RFR: 8255216: ciEnv::_break_at_compile isn't in use

[Dan]

_break_at_compile is no longer in use and can be safely removed.
No new code, and Tier1 tests succeed after code is removed.

Bug: https://bugs.openjdk.java.net/browse/JDK-8255216

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Commit messages:
 - 8255216: ciEnv::_break_at_compile isn't in use

Changes: https://git.openjdk.java.net/jdk/pull/1806/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1806&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255216
  Stats: 11 lines in 3 files changed: 0 ins; 11 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1806.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1806/head:pull/1806

PR: https://git.openjdk.java.net/jdk/pull/1806