RFR: 8283846: Remove unused jdk.internal.reflect.SignatureIterator

[Andrey Turbanov]

It was no longer used due to JDK-4479184 long ago.

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Commit messages:
 - [PATCH] Remove unused jdk.internal.reflect.SignatureIterator

Changes: https://git.openjdk.java.net/jdk/pull/8013/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8013&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283846
  Stats: 81 lines in 1 file changed: 0 ins; 81 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8013.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8013/head:pull/8013

PR: https://git.openjdk.java.net/jdk/pull/8013