Remove unused init file and directory

Nova contained v2 and v3 APIs as its history, but now v3 API has
been removed. tempest/api/compute/v2 directory was added for separating
tests between v2 and v3, but now it becomes unnecessary.
So this patch removes it for cleanup.

Change-Id: I58460fb625923a5533635d025e32c89ffd3733c3
1 file changed