RFR: 8265867: thread.hpp defines some enums but no reference [v2]

[Xin Liu]

> Deleted 2 useless enums.
> This patch also added const and constexpr for the applicable member functions.

Xin Liu has updated the pull request incrementally with one additional commit since the last revision:

  Revert code change about "constness".

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3702/files
  - new: https://git.openjdk.java.net/jdk/pull/3702/files/830ae1a3..244b5aa0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3702&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3702&range=00-01

  Stats: 92 lines in 4 files changed: 0 ins; 0 del; 92 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3702.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3702/head:pull/3702

PR: https://git.openjdk.java.net/jdk/pull/3702