RFR: 8300872: WebView's ColorChooser fails to initialize when running in security context

[Jose Pereda]

This PR removes an unnecessary check that was added as part of [JDK-8267551](https://bugs.openjdk.org/browse/JDK-8267551).

As commented in the [issue](https://bugs.openjdk.org/browse/JDK-8300872), there were no failing/passing tests before/after these lines were added, and there are no actual tests that get into the case.

The mentioned check caused, as a side effect, the JDK-8300872 issue, as running under a (deprecated) security manager fails with:

java.security.AccessControlException: access denied ("java.io.FilePermission" "jrt:/javafx.controls/com/sun/javafx/scene/control/skin/modena/pattern-transparent.png" "read")
...
at javafx.graphics/javafx.scene.image.Image.validateUrl(Image.java:1127)
...

when `File::exists` is evaluated over an image bundled in a jar.

-------------

Commit messages:
 - Remove unneeded check

Changes: https://git.openjdk.org/jfx/pull/1042/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1042&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300872
  Stats: 6 lines in 1 file changed: 0 ins; 5 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1042.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/1042/head:pull/1042

PR: https://git.openjdk.org/jfx/pull/1042