RFR: 8254771: Remove unimplemented ciSignature::get_all_klasses

[Aleksey Shipilev]

This method is not implemented, and there was no definition since the initial load. Can be removed.

Testing:
  - [x] Linux x86_64 build
  - [x] Text search for `get_all_klasses` in `src/hotspot`; there is `JdkJfrEvent::get_all_klasses` that looks unrelated.

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Commit messages:
 - 8254771: Remove unimplemented ciSignature::get_all_klasses

Changes: https://git.openjdk.java.net/jdk/pull/657/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=657&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254771
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/657.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/657/head:pull/657

PR: https://git.openjdk.java.net/jdk/pull/657