btrfs-progs: mark static & remove unused from shared kernel code

btrfs-progs: mark static & remove unused from shared kernel code

In files copied from the kernel, mark many functions as static,
and remove any resulting dead code.

Some functions are left unmarked if they aren't static in the
kernel tree.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>