RFR: 8316357: Serial: Remove unused GenCollectedHeap::space_containing

[Albert Mingkun Yang]

Trivial removing dead code.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/15760/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15760&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316357
  Stats: 22 lines in 4 files changed: 0 ins; 22 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15760.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15760/head:pull/15760

PR: https://git.openjdk.org/jdk/pull/15760