RFR: 8296479: Remove stray comment about POST_STRIP_CMD

[Magnus Ihse Bursie]

The variable POST_STRIP_CMD has been removed, but not all comments about it

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Commit messages:
 - 8296479: Remove stray comment about POST_STRIP_CMD

Changes: https://git.openjdk.org/jdk/pull/11021/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11021&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296479
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11021.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11021/head:pull/11021

PR: https://git.openjdk.org/jdk/pull/11021