Remove depreciated PyTest settings

Looponfailroots used to be required for some functionality in PyTest,
but the option was silently depreciated recently in PyTest and will now
cause failures. It's safe to remove now though, so it just is.

Author: markjonestx

setup.cfg

@@ -4,8 +4,5 @@ universal = 1
 [tool:pytest]
 norecursedirs=test_data/
 addopts = --cov=PyPWA --no-cov-on-fail
-looponfailroots =
-    PyPWA
-    tests
 testpaths =
     tests