removing fiemap logic from copy.c

[Pádraig Brady]

FYI tomorrow I'm going to push a change to
remove the fiemap extent handling logic from cp/mv/install etc.
(Assuming that ok with folks of course).

This is only used on 10 year old linux kernels,
(where SEEK_HOLE is not available).

Also with fiemap we perform an fsync before each copy,
which is best avoided.

The patch is largish, but boring as just removes lines,
so not attaching here.

Will reply with a link when pushed.

cheers,
Pádraig