RFR: 8333962: Obsolete OldSize

[Albert Mingkun Yang]

Obsolete OldSize and related code. An internal variable `OldSize` is kept to capture the capacity of old-gen size.

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Commit messages:
 - obsolete-old-size

Changes: https://git.openjdk.org/jdk/pull/19647/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19647&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333962
  Stats: 193 lines in 15 files changed: 8 ins; 168 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/19647.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19647/head:pull/19647

PR: https://git.openjdk.org/jdk/pull/19647