Undo recent _FILE_OFFSET_BITS=64 changes.

We had several bugs filed saying "if I set _FILE_OFFSET_BITS=64 when
targeting an API < L, various functions are missing". Instead of
saying "yes, they are", we quietly just modified the header files to
expose the non-64-bit variants. This makes no sense. We can't just say
"oh, yeah, we don't have a version of this function that agrees with
your calling code about how large off_t is, but here's a version that
doesn't: I'm sure it'll be fine".

_FILE_OFFSET_BITS=64 on Android LP32 has always been a game of chance,
but that game should be "are all the functions my code needs available
at compile time?", not "will my code actually work at run time?".

Bug: https://github.com/android-ndk/ndk/issues/449
Bug: https://github.com/android-ndk/ndk/issues/442
Bug: https://github.com/android-ndk/ndk/issues/333
Bug: https://github.com/android-ndk/ndk/issues/332
Bug: https://github.com/android-ndk/ndk/issues/324
Test: builds
Change-Id: Ib095251d3e21e77ed50cc3575388107fecec4ecd