Verify OpenJDK 8u121: some java.io File classes

FileInputStream, FileOutputStream, FileSystem:
 - improved change markers
 - removed some SecurityManager docs from FileOutputStream for
   consistency with FileInputStream
 - Code reordering for consistency with upstream

No functional changes.

Bug: 35910877
Test: build
Change-Id: I0c8dea246432c626c0f969f9b205ec05ac176606