RFR: 8371087: Remove unused dependency on jdk.unsupported from javafx.graphics

[Kevin Rushforth]

This PR removes the unused dependency on `jdk.unsupported` from `javafx.graphics` as a followup to [JDK-8334137](https://bugs.openjdk.org/browse/JDK-8334137), which replaced the use of `sun.misc.Unsafe` with FFM in PR #1814. `sun.misc.Unsafe` was the only use of `jdk.unsupported`, so it can now be removed.

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Commit messages:
 - 8371087: Remove unused dependency on jdk.unsupported from javafx.graphics

Changes: https://git.openjdk.org/jfx/pull/1957/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1957&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371087
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1957.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1957/head:pull/1957

PR: https://git.openjdk.org/jfx/pull/1957