Remove unused method inject_file()

Remove the unused method, inject_file(), from the compute.api and
compute.rpcapi.  mark it deprecated on the manager side to be removed on the
next major iteration of the compute rpc interface.

Related to blueprint virt-objects

Change-Id: I53339e39604f90cf7ecf159da78c4e8e9283bf87
Merge "Remove unused method inject_file()"