Remove redundant body validation for createBackup

The body validation is redundant for createBackup, should remove it. In
fact that this extension is registered as WSGI action implies that the
body must contain a key with the same name as action.

Change-Id: I327688b2df50782bc38b97a4750f83a607623ce4
Closes-Bug: #1254988
Merge "Remove redundant body validation for createBackup"