RFR: 8341619: C2: remove unused StoreCM node

Tue Oct 8 07:02:50 UTC 2024

This cleanup removes C2's `StoreCM` (store card mark) node and all its special handling code. This node used to model card mark stores in early-expanded G1 post-barriers, and is no longer needed after [JEP 475](https://openjdk.org/jeps/475).

__Testing:__ tier1-5 (linux-x64, linux-aarch64, windows-x64, macosx-x64, and macosx-aarch64; release and debug mode).

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Commit messages:
 - Remove StoreCM node

Changes: https://git.openjdk.org/jdk/pull/21385/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21385&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341619
  Stats: 388 lines in 23 files changed: 0 ins; 376 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/21385.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21385/head:pull/21385

PR: https://git.openjdk.org/jdk/pull/21385