RFR: 8329470: Remove obsolete CDS SharedStrings tests

[Ioi Lam]

These tests are quite time consuming. Removing them will speed up the CDS tests cycle.

[1] The LockSharedStrings.java test is obsolete. The archived strings used to be in its own "special" G1 region and we needed a test to check if locking objects in this region is working properly. Today all archived heap objects are stored in regular G1 regions. This test is no longer needed.

[2] During CDS dump time, we no longer allocate extra copies of the archived heap objects in the actual Java heap. So we can removed the portion of SharedStringsStress.java that tests for "an extra copy of these objects are allocated".

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Commit messages:
 - 8329470: Remove obsolete CDS SharedStrings tests

Changes: https://git.openjdk.org/jdk/pull/18573/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18573&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329470
  Stats: 253 lines in 4 files changed: 5 ins; 241 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/18573.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18573/head:pull/18573

PR: https://git.openjdk.org/jdk/pull/18573