RFR: 8339399: ZGC: Remove unnecessary page reset when splitting pages

[Joel Sikström]

There is no use-case where it is necessary to reset the same page after splitting and thus the reset should be removed.

Tested with tiers 1-3.

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Commit messages:
 - 8339399: ZGC: Remove unnecessary page reset when splitting pages

Changes: https://git.openjdk.org/jdk/pull/20824/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20824&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339399
  Stats: 11 lines in 2 files changed: 1 ins; 10 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20824.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20824/head:pull/20824

PR: https://git.openjdk.org/jdk/pull/20824