e4defrag: remove a lot of cruft

e4defrag: remove a lot of cruft

e4defrag.c had a lot of stuff copied into it from other
places, redefinitions of existing interfaces, etc.

We should be able to remove most of this, as the tool only
works on recent kernels anyway, we should just pick up
definitions from recent kernel headers whenever possible.

I've left the local definitions of fallocate, fadvise
(changed to posix_fadvise) and sync_file_range, and
wrapped them in #ifdef configure-time tests - though
really it seems like only fallocate should be necessary
by now, and perhaps the others can be dropped.

We still need some Makefile work so that it won't try to
build e4defrag if the right pieces aren't there (and
if the local definitions won't work...)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>