RFR: 8275413: Remove unused InstanceKlass::set_array_klasses() method

[Zhengyu Gu]

Please review this trivial patch that removes unused nstanceKlass::set_array_klasses() method.

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Commit messages:
 - v0

Changes: https://git.openjdk.java.net/jdk/pull/5991/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5991&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275413
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5991.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5991/head:pull/5991

PR: https://git.openjdk.java.net/jdk/pull/5991