Remove unused methods File{Input,Output}Stream.open().

Also removes the related native code.

These open() methods are no longer used due to
https://r.android.com/725443 and are private with no unsupported
app usage.

Bug: 112107427
Test: atest CtsLibcoreTestCases
Change-Id: I0e4ec21a0686eb151d2da2eb0c11def70921b3e9
6 files changed