RFR: 8294608: Remove redundant unchecked suppression in FileDescriptor

[Alan Bateman]

On Wed, 28 Sep 2022 20:39:03 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> Found this redundant suppressions by IntelliJ IDEA inspection.
> It seems [JDK-8189330](https://bugs.openjdk.org/browse/JDK-8189330) made them redundant.

Marked as reviewed by alanb (Reviewer).

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PR: https://git.openjdk.org/jdk/pull/10473