RFR: 8321122: Shenandoah: Remove ShenandoahLoopOptsAfterExpansion flag

[Aleksey Shipilev]

More flags cleanup. `ShenandoahLoopOptsAfterExpansion` was added long time ago to gate more aggressive barrier optimizations in C2. It was default since then. There seem to be no reason to keep it as the flag. Just checking, @rwestrel -- you don't need it anymore, right?

Additional testing:
 - [x] `hotspot_gc_shenandoah`

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Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/16908/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16908&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321122
  Stats: 18 lines in 2 files changed: 5 ins; 11 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16908.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16908/head:pull/16908

PR: https://git.openjdk.org/jdk/pull/16908