RFR: 8285364: Remove REF_ enum for java.lang.ref.Reference [v8]

[Albert Mingkun Yang]

> Simple rename and some comments update.
> 
> Test: build

Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:

  fix build

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/8332/files
  - new: https://git.openjdk.org/jdk/pull/8332/files/3fa67ab2..b1c0369a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=8332&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=8332&range=06-07

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/8332.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/8332/head:pull/8332

PR: https://git.openjdk.org/jdk/pull/8332