btrfs-tools: Do not use 64bit functions for largefile support

Using -D_FILE_OFFSET_BITS=64 already makes the normal function behave
like 64bit variants. Moreover it makes them portable across libc

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>