RFR: 8335544: Serial: Remove unused _should_allocate_from_space

[Albert Mingkun Yang]

Trivial removing dead code.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/19988/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19988&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335544
  Stats: 13 lines in 2 files changed: 0 ins; 13 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19988.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19988/head:pull/19988

PR: https://git.openjdk.org/jdk/pull/19988