RFR: 8345796: Backout doc change introduced by JDK-8235786

[Michael McMahon]

This change backs out the API doc change in com.sun.net.httpserver.HttpExchange introduced by JDK-8235786.

It is a straight git revert of that commit. We will address the original issue in a different way in 25

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Commit messages:
 - Revert "8235786: Javadoc for com/sun/net/httpserver/HttpExchange.java#setAttribute is unclear"

Changes: https://git.openjdk.org/jdk/pull/22639/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22639&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345796
  Stats: 131 lines in 2 files changed: 5 ins; 108 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/22639.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22639/head:pull/22639

PR: https://git.openjdk.org/jdk/pull/22639