RFR: 8378298: Remove obsolete CDS string tests

[Ioi Lam]

There are some very basic String test cases that came from early CDS development. They don't serve any purposes anymore as the functionalities are already covered by other test cases.

The methods of `WhiteBox.{areSharedStringsMapped, isSharedInternedString}` do not work for `AOTStreamedHeapLoader`, whose design doesn't distinguish between strings that came from the CDS archive or the app. The test cases that use these methods don't seem to be worth keeping.

`DumpSymbolAndStringTable` should be simplified to only test for `VM.stringtable` and `VM.symboltable`. The boiler-plate tests for `VM.systemdictionary` should be removed as we already have a more elaborate test: `serviceability/dcmd/vm/DictionaryStatsTest.java`.

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Commit messages:
 - 8378298: Remove obsolete CDS string tests

Changes: https://git.openjdk.org/jdk/pull/29834/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29834&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378298
  Stats: 843 lines in 17 files changed: 2 ins; 831 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/29834.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29834/head:pull/29834

PR: https://git.openjdk.org/jdk/pull/29834