Clean up test PDF references

I've attempted to clean up the test PDF data so that there are no warnings or errors when getting the test reference files.

The general strategy I applied was as follows:

* If there was an error (the file couldn't be retrieved):
 1. Try a Web Archive copy from some date before the commit that added it
 2. If that failed, remove it from the list of tests
* If there was an warning (the MD5 hash doesn't match):
 1. Try a Web Archive copy from some date before the commit that added it
 2. If still not matching, examine the goal of the commit and accept new hash if test file still demonstrates the same problem
 3. If that failed, remove it from the list of tests