RFR: 8343703: Symbol name cleanups after JEP 479

[David Holmes]

After JEP 479 ([JDK-8339783](https://bugs.openjdk.org/browse/JDK-8339783) was integrated, the handling of certain symbol lookup code can be simplified. The old code needed to support 32-bit Windows, where names had a trailing `@<number>`. When this special case now is removed, some streamlining is possible. Specifically these arrays:

#define JNI_ONLOAD_SYMBOLS {"JNI_OnLoad"}
#define JNI_ONUNLOAD_SYMBOLS {"JNI_OnUnload"}
#define JVM_ONLOAD_SYMBOLS {"JVM_OnLoad"}
#define AGENT_ONLOAD_SYMBOLS {"Agent_OnLoad"}
#define AGENT_ONUNLOAD_SYMBOLS {"Agent_OnUnload"}
#define AGENT_ONATTACH_SYMBOLS {"Agent_OnAttach"}

are all singletons and so the actual strings can just be inlined directly into the code that uses them.

Testing:
- GHA
- Tiers 1-4 sanity
- 
Thanks

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Commit messages:
 - 8343703: Symbol name cleanups after JEP 479

Changes: https://git.openjdk.org/jdk/pull/22380/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22380&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343703
  Stats: 95 lines in 5 files changed: 7 ins; 49 del; 39 mod
  Patch: https://git.openjdk.org/jdk/pull/22380.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22380/head:pull/22380

PR: https://git.openjdk.org/jdk/pull/22380