RFR: 8344896: Remove obsolete checks for AWTPermission accessClipboard

[Phil Race]

This removes the SecurityManager related checks for clipboard access  and methods which exist solely to support that.

One interesting thing is that there are two places where a method "canAccessSystemClipboard()"  was not only about the SM. 
In SwingUtilities and InputEvent it would return false in headless mode, regardless of whether there is an SM.
This means I have left the methods in place, behaving the same as before in headless mode.
We may be able to further simplify this later  but it will be clearer with the SM-only logic removed and out of scope for this fix.

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Commit messages:
 - 8344896

Changes: https://git.openjdk.org/jdk/pull/22356/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22356&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344896
  Stats: 277 lines in 11 files changed: 1 ins; 267 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/22356.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22356/head:pull/22356

PR: https://git.openjdk.org/jdk/pull/22356