btrfs-progs: drop unused parameter from btrfs_release_path

btrfs-progs: drop unused parameter from btrfs_release_path

Port of commit b3b4aa7 to userspace.

parameter tree root it's not used since commit
5f39d397dfbe140a14edecd4e73c34ce23c4f9ee ("Btrfs: Create extent_buffer
interface for large blocksizes")

This gets userspace a tad closer to kernelspace by removing
this unused parameter that was all over the codebase...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>