bpo-42392: Remove loop parameter from asyncio.streams (GH-23517)

diff --git a/Lib/asyncio/streams.py b/Lib/asyncio/streams.py
index 3c80bb8..96a9f97 100644
--- a/Lib/asyncio/streams.py
+++ b/Lib/asyncio/streams.py
@@ -23,7 +23,7 @@
 
 
 async def open_connection(host=None, port=None, *,
-                          loop=None, limit=_DEFAULT_LIMIT, **kwds):
+                          limit=_DEFAULT_LIMIT, **kwds):
     """A wrapper for create_connection() returning a (reader, writer) pair.
 
     The reader returned is a StreamReader instance; the writer is a
@@ -41,12 +41,7 @@ async def open_connection(host=None, port=None, *,
     StreamReaderProtocol classes, just copy the code -- there's
     really nothing special here except some convenience.)
     """
-    if loop is None:
-        loop = events.get_event_loop()
-    else:
-        warnings.warn("The loop argument is deprecated since Python 3.8, "
-                      "and scheduled for removal in Python 3.10.",
-                      DeprecationWarning, stacklevel=2)
+    loop = events.get_running_loop()
     reader = StreamReader(limit=limit, loop=loop)
     protocol = StreamReaderProtocol(reader, loop=loop)
     transport, _ = await loop.create_connection(
@@ -56,7 +51,7 @@ async def open_connection(host=None, port=None, *,
 
 
 async def start_server(client_connected_cb, host=None, port=None, *,
-                       loop=None, limit=_DEFAULT_LIMIT, **kwds):
+                       limit=_DEFAULT_LIMIT, **kwds):
     """Start a socket server, call back for each client connected.
 
     The first parameter, `client_connected_cb`, takes two parameters:
@@ -78,12 +73,7 @@ async def start_server(client_connected_cb, host=None, port=None, *,
     The return value is the same as loop.create_server(), i.e. a
     Server object which can be used to stop the service.
     """
-    if loop is None:
-        loop = events.get_event_loop()
-    else:
-        warnings.warn("The loop argument is deprecated since Python 3.8, "
-                      "and scheduled for removal in Python 3.10.",
-                      DeprecationWarning, stacklevel=2)
+    loop = events.get_running_loop()
 
     def factory():
         reader = StreamReader(limit=limit, loop=loop)
@@ -98,14 +88,10 @@ def factory():
     # UNIX Domain Sockets are supported on this platform
 
     async def open_unix_connection(path=None, *,
-                                   loop=None, limit=_DEFAULT_LIMIT, **kwds):
+                                   limit=_DEFAULT_LIMIT, **kwds):
         """Similar to `open_connection` but works with UNIX Domain Sockets."""
-        if loop is None:
-            loop = events.get_event_loop()
-        else:
-            warnings.warn("The loop argument is deprecated since Python 3.8, "
-                          "and scheduled for removal in Python 3.10.",
-                          DeprecationWarning, stacklevel=2)
+        loop = events.get_running_loop()
+
         reader = StreamReader(limit=limit, loop=loop)
         protocol = StreamReaderProtocol(reader, loop=loop)
         transport, _ = await loop.create_unix_connection(
@@ -114,14 +100,9 @@ async def open_unix_connection(path=None, *,
         return reader, writer
 
     async def start_unix_server(client_connected_cb, path=None, *,
-                                loop=None, limit=_DEFAULT_LIMIT, **kwds):
+                                limit=_DEFAULT_LIMIT, **kwds):
         """Similar to `start_server` but works with UNIX Domain Sockets."""
-        if loop is None:
-            loop = events.get_event_loop()
-        else:
-            warnings.warn("The loop argument is deprecated since Python 3.8, "
-                          "and scheduled for removal in Python 3.10.",
-                          DeprecationWarning, stacklevel=2)
+        loop = events.get_running_loop()
 
         def factory():
             reader = StreamReader(limit=limit, loop=loop)