RFR: 8298145: Remove ContiguousSpace::capacity

[Albert Mingkun Yang]

Trivial change of removing redundant code.

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Commit messages:
 - s1-remove-sub-impl

Changes: https://git.openjdk.org/jdk/pull/11528/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11528&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8298145
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11528.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11528/head:pull/11528

PR: https://git.openjdk.org/jdk/pull/11528