RFR: 8358313: G1: Refactor G1CollectedHeap::is_maximal_no_gc

[Albert Mingkun Yang]

Simple changing of a method name and return-type to be more consistent with the surrounding code.

Test: tier1

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Commit messages:
 - g1-rename

Changes: https://git.openjdk.org/jdk/pull/25579/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25579&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358313
  Stats: 10 lines in 2 files changed: 3 ins; 4 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/25579.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25579/head:pull/25579

PR: https://git.openjdk.org/jdk/pull/25579