Remove unused WebKit files

As part of the 606.1 WebKit upgrade, several unused files were removed. The 8u backport removed an additional 336 files that are still present in jfx-dev. In a continued effort to keep the native webkit code in sync, we should remove these files unless there is a compelling reason to keep them in jfx-dev (in which case we should restore them in 8u-dev).

See the attached list of files that are present in jfx-dev/rt/modules/javafx.web/src/main/native, but have been removed from 8u-dev/rt/modules/web/src/main/native