RFR: 8251495: Clarify DOM documentation

[Joe Wang]

Revert changes made by JDK-8249643, removing the implNote.

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Commit messages:
 - 8251495: Clarify DOM documentation

Changes: https://git.openjdk.java.net/jdk/pull/100/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=100&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251495
  Stats: 25 lines in 1 file changed: 0 ins; 25 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/100.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/100/head:pull/100

PR: https://git.openjdk.java.net/jdk/pull/100