RFR: 8262296 Fix remaining doclint warnings in jdk.httpserver

[Chris Hegarty]

Trivial clean up of remaining doclint warnings in jdk.httpserver. 

The minor spec clarifications do not amount to a normative change, so no CSR is required (they're documented the obvious and only possible behaviour).

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Commit messages:
 - Initial changes

Changes: https://git.openjdk.java.net/jdk/pull/2706/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2706&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262296
  Stats: 5 lines in 4 files changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2706.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2706/head:pull/2706

PR: https://git.openjdk.java.net/jdk/pull/2706