RFR: 8256738: Compiler interface clean-up

[Claes Redestad]

This patch removes dead code in the ci area.

There's also a trivial micro-optimization to is_boxing_method/is_unboxing_method

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Commit messages:
 - instanceOop include needed for assert
 - Compiler interface clean-up

Changes: https://git.openjdk.java.net/jdk/pull/1345/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1345&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256738
  Stats: 216 lines in 21 files changed: 0 ins; 211 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1345.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1345/head:pull/1345

PR: https://git.openjdk.java.net/jdk/pull/1345