RFR: 8276298: G1: Fix or remove G1SegmentedArrayBufferList::add [v2]

[Hamlin Li]

> This is minor removal of unused method G1SegmentedArrayBufferList::add.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Add assert

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6223/files
  - new: https://git.openjdk.java.net/jdk/pull/6223/files/b3c46246..b48a4e4d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6223&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6223&range=00-01

  Stats: 2 lines in 2 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6223.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6223/head:pull/6223

PR: https://git.openjdk.java.net/jdk/pull/6223