RFR: Fixed backing out a backport

[Jesper Wilhelmsson]

Backing out a change was updated to not use sub-tasks, but the similar case of backing out a backport was missed.

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Commit messages:
 - Fixed word
 - Fixed backing out a backport

Changes: https://git.openjdk.org/guide/pull/160/files
  Webrev: https://webrevs.openjdk.org/?repo=guide&pr=160&range=00
  Stats: 23 lines in 2 files changed: 5 ins; 4 del; 14 mod
  Patch: https://git.openjdk.org/guide/pull/160.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/160/head:pull/160

PR: https://git.openjdk.org/guide/pull/160