RFR: 8296262: Remove dead code from InstanceKlass::signature_name()

[David Holmes]

Trivial dead code removal.

Testing: simple build.

Thanks.

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Commit messages:
 - 8296262: Remove dead code from InstanceKlass::signature_name()

Changes: https://git.openjdk.org/jdk/pull/10962/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10962&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296262
  Stats: 8 lines in 1 file changed: 0 ins; 7 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10962.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10962/head:pull/10962

PR: https://git.openjdk.org/jdk/pull/10962