RFR: 8290290: Remove addition of TimeInstants [v2]

[Kim Barrett]

> Please review this trivial change to remove the unused and semantically suspect
> function TimeInstant::operator+(TimeInstant).

Kim Barrett has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into no-add-ticks
 - remove addition of TimeInstants

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9489/files
  - new: https://git.openjdk.org/jdk/pull/9489/files/21b10028..f083e572

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9489&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9489&range=00-01

  Stats: 28 lines in 2 files changed: 6 ins; 18 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/9489.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9489/head:pull/9489

PR: https://git.openjdk.org/jdk/pull/9489