Remove CopyNode (#2244)

Summary:
Pull Request resolved: #2244

`CopyNode` simply copies data from one image texture to another image texture of the same size.

During inception of the graph runtime, it was useful to validate that components were working, but won't serve us any use in the future.
ghstack-source-id: 217394065
exported-using-ghexport

Reviewed By: SS-JIA

Differential Revision: D54369109

fbshipit-source-id: bdc63ca302e552bed742da0b59c8a848f44d1273

Author: jorgep31415