R1:81e4e5b7f9c9

Remove construction of "author" information from "LastModified" payload in Diffusion

Summary:
Ref T13552. When viewing a directory in Diffusion, we make an Ajax call to get the last commit for each path.

This call currently pulls author information, since an older version of this UI showed author information.

The current UI does not show author information, so this parameter is unused. Delete the code which builds it.

Test Plan: Grepped for `'author'` and references to the "pull-lastmodified" behavior.