RFR: 8344181: Remove SecurityManager and related calls from jdk.management and jdk.management.agent

[Kevin Walls]

Remove redundant SecurityManager, AccessController references
(following on from JDK-8338411: Implement JEP 486: Permanently Disable the Security Manager).

src/jdk.management/share/classes/com/sun/management/internal/GarbageCollectionNotifInfoCompositeData.java
There is an existing theoretical path where GcInfoBuilder stays null, should never happen, "com.sun.management.GcInfo" exists...

src/jdk.management/share/classes/com/sun/management/internal/GcInfoCompositeData.java
Similarly there is an existing assumption that Class.forName("com.sun.management.GcInfo") succeeds.

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Commit messages:
 - oops
 - 8344181: Remove SecurityManager and related calls from jdk.management and jdk.management.agent

Changes: https://git.openjdk.org/jdk/pull/22155/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22155&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344181
  Stats: 119 lines in 9 files changed: 0 ins; 78 del; 41 mod
  Patch: https://git.openjdk.org/jdk/pull/22155.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22155/head:pull/22155

PR: https://git.openjdk.org/jdk/pull/22155