jmx-dev RFR: 8347345: Remove redundant test policy file from ModelMBeanInfoSupport directory

[Kevin Walls]

A redundant policy file exists, it is unused and must have been missed during:
8338411: Implement JEP 486: Permanently Disable the Security Manager

Test in test/jdk/javax/management/modelmbean/ModelMBeanInfoSupport still passes after this change.

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Commit messages:
 - remove old policy file

Changes: https://git.openjdk.org/jdk/pull/23002/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23002&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347345
  Stats: 14 lines in 1 file changed: 0 ins; 14 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23002.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23002/head:pull/23002

PR: https://git.openjdk.org/jdk/pull/23002