RFR: 8359664: G1: Remove default arg for pretouch_workers of G1CollectedHeap::expand

[Albert Mingkun Yang]

Trivial removing unnecessary default arg value.

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Commit messages:
 - g1-trivial-remove-default-arg

Changes: https://git.openjdk.org/jdk/pull/25826/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25826&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359664
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25826.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25826/head:pull/25826

PR: https://git.openjdk.org/jdk/pull/25826