RFR: 8367409: G1: Remove unused G1MonotonicArena::Segment::copy_to()

[Leo Korinth]

The code compiles.

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Commit messages:
 - revert autoformat mistake
 - keep a newline between delete_segment and is_full()
 - 8367409: G1: Remove unused G1MonotonicArena::Segment::copy_to()

Changes: https://git.openjdk.org/jdk/pull/27221/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27221&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367409
  Stats: 6 lines in 1 file changed: 0 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27221.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27221/head:pull/27221

PR: https://git.openjdk.org/jdk/pull/27221