RFR: 8342459: Remove calls to doPrivileged in javafx.base

[Ambarish Rapte]

Remove `doPrivileged` calls in the javafx.base module.
The changes are straight forward.
1. Remove doPrivileged calls, with keeping the lambda expression.
2. Remove SuppressWarnings annotations
3. Remove unused imports

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Commit messages:
 - rm doPrivileged in javafx.base

Changes: https://git.openjdk.org/jfx/pull/1625/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1625&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342459
  Stats: 376 lines in 20 files changed: 17 ins; 159 del; 200 mod
  Patch: https://git.openjdk.org/jfx/pull/1625.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1625/head:pull/1625

PR: https://git.openjdk.org/jfx/pull/1625