Remove explicit #define of _FILE_OFFSET_BITS

Remove explicit #define of _FILE_OFFSET_BITS

The problem with explicitly setting _FILE_OFFSET_BITS is that
it's not necessarily a no-op on a 64-bit platform with a 64-bit off_t.
Apparently glibc's mips64el which end up using a different structure
definition for struct stat, and this causes a compatibility problem
with libarchive.  It's not needed on mips64el, since off_t is 64-bits,
but it actually causes problems.

So remove it, since we now use the autoconf's AC_SYS_LARGEFILE, which
will set _FILE_OFFSET_BITS when it is necessary (such as on a 32-bit
i386 Linux platform), and will skip it when it is unnecessary.

Addresses-Debian-Bug: #1070042
Signed-off-by: Theodore Ts'o <tytso@mit.edu>