RFR: Disable assertions in code that is expected to be replaced soon

[William Kemper]

The lack of these assertions has not caused problems for release builds in performance tests. We expect this code to be replaced soon so we are disabling these assertions before we become inured to test failures.

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

Commit messages:
 - Disable assertions in code that is expected to be replaced soon

Changes: https://git.openjdk.org/shenandoah/pull/256/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=256&range=00
  Stats: 6 lines in 2 files changed: 3 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/shenandoah/pull/256.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/256/head:pull/256

PR: https://git.openjdk.org/shenandoah/pull/256