RFR: JDK-8280393: Promote use of HtmlTree factory methods [v2]

[Hannes Wallnöfer]

> This is a simple cleanup to add and/or make use of `HtmlTree` factory methods for `UL` and `DIV` with a single `HtmlStyle` parameter.
> 
> There are no test changes (noreg-cleanup) and no changes in the generated JDK documentation.

Hannes Wallnöfer has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8280393: Remove unnecessary class attribute

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7162/files
  - new: https://git.openjdk.java.net/jdk/pull/7162/files/6a658676..40373b11

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7162&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7162&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7162.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7162/head:pull/7162

PR: https://git.openjdk.java.net/jdk/pull/7162