storage: fix signed url tests. fixes #238

- Removed the regression test
- Added a test that the expiration date we passed was honored by our code. Whether that's honored upstream or not is in the hands of another library's code :)
Updated. That's my usual style as well, however we were using the 4 space continuation style in the library. I haven't found any kind of official rules of when to indent 4 vs 2 on a new line, so 2 works for me :)