RFR: Removed forwardporting

[Jesper Wilhelmsson]

@edvbld is out for the next few months so on his request I took over the change from #105. I have updated the patch based on the changes I proposed in my review there.

This patch removes the instructions related to forwardporting as this is no longer a concept in OpenJDK.

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Commit messages:
 - Removed forwardporting

Changes: https://git.openjdk.org/guide/pull/107/files
 Webrev: https://webrevs.openjdk.org/?repo=guide&pr=107&range=00
  Stats: 25 lines in 2 files changed: 4 ins; 19 del; 2 mod
  Patch: https://git.openjdk.org/guide/pull/107.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/107/head:pull/107

PR: https://git.openjdk.org/guide/pull/107