RFR: 8272777: Clean up remaining AccessController warnings in test library

[Kevin Walls]

Reduce noise in test output by adding the @SuppressWarnings("removal") annotation (which has already been widely applied).

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Commit messages:
 - 8272777: Clean up remaining AccessController warnings in test library

Changes: https://git.openjdk.java.net/jdk/pull/7328/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7328&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272777
  Stats: 5 lines in 3 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7328.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7328/head:pull/7328

PR: https://git.openjdk.java.net/jdk/pull/7328