[lworld] RFR: 8346305: [lworld] Revert WeakHashMap POC for a value object policy

[Roger Riggs]

Remove the proof of concept for a ValuePolicy that would allow value objects to be put in WeakHashMap by using a proxy object.
The feature is not being adopted at this time.
Remove test/jdk/valhalla/valuetypes/WeakValuePolicyTest.java

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

Commit messages:
 - 8346305: [lworld] Revert WeakHashMap POC for a value object policy

Changes: https://git.openjdk.org/valhalla/pull/1320/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1320&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346305
  Stats: 482 lines in 4 files changed: 1 ins; 476 del; 5 mod
  Patch: https://git.openjdk.org/valhalla/pull/1320.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1320/head:pull/1320

PR: https://git.openjdk.org/valhalla/pull/1320