Remove asyncio_default_fixture_loop_scope setting (#1205)

The behavior of the default value of
`asyncio_default_fixture_loop_scope` changed in Pytest 1.2.0. Now
setting it to "function" results in an error. Removing the setting from
`pytest.ini` makes things work again.

Author: mhucka

dev_tools/conf/pytest.ini

@@ -16,8 +16,5 @@
 markers =
     slow: marks tests as slow (deselect with '-m "not slow"')
 
-# Silence deprecation warnings about option "asyncio_default_fixture_loop_scope"
-asyncio_default_fixture_loop_scope = "function"
-
 filterwarnings =
     ignore:Skipped assert_qasm_is_consistent_with_unitary because qiskit.*:UserWarning