tests: Remove {old,new}.file.

They serve the same purpose as {boot,recovery}.img, except that they're
not structured to be imgdiff'd. Remove the two files and replace all the
uses with {boot,recovery}.img instead.

Bug: 110106408
Test: Run recovery_{unit,component}_test on marlin.
Change-Id: I8e71187d5b0c142ad932f33717f6fae364b43abc