RFR: 8285951: Replace Algorithms.eatMemory(...) with WB.fullGC() in vmTestbase_vm_gc_ref tests

[Leonid Mesnik]

remainging weak/soft/phantom reference tests are updated to use WB.fullGC()

The TEST.properties are removed for single-threaded tests.

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Commit messages:
 - fix

Changes: https://git.openjdk.java.net/jdk/pull/8474/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8474&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285951
  Stats: 986 lines in 28 files changed: 166 ins; 621 del; 199 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8474.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8474/head:pull/8474

PR: https://git.openjdk.java.net/jdk/pull/8474