Revert D26641600: [caffe2] move the SaveOp implementation from a header to a .cc file
Test Plan: revert-hammer
Differential Revision:
D26641600 (https://github.com/pytorch/pytorch/commit/3969391c0732bd1e6329438664dba3d7f5ee74b7)
Original commit changeset: 84ebe8164ffa
fbshipit-source-id: c3a85b7b15b8cdbf019abfabfd740a5b1d5e8775
