RFR: 8279361: Error in documentation of third Stream.reduce method [v2]

[Viktor Klang]

> This JavaDoc change attempts to shine some light on the `combiner`-function as it relates to the third variant of `Stream.reduce` since it according to the bug submission in JBS can be confusing that the `combiner` is not mentioned in the code example in the documentation.

Viktor Klang has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8279361 - Error in documentation of third Stream.reduce method
  
  Removes the partial pseudo-code which omitted the details regarding the `combiner`
  as it was deemed confusing.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10469/files
  - new: https://git.openjdk.org/jdk/pull/10469/files/9bdd85b7..5f93e779

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10469&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10469&range=00-01

  Stats: 47 lines in 4 files changed: 0 ins; 42 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/10469.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10469/head:pull/10469

PR: https://git.openjdk.org/jdk/pull/10469