json: mark keyword-only args, remove deprecated arg (#3756)

* json: mark keyword-only args

Technically only true for Python 3.6+, but I didn't feel like copying
over the whole file just for Python 3.5. Let me know and I can.

* json: remove encoding from loads

This has been ignored and deprecated since 3.1 and will be removed in 3.9
It no longer even shows up in inspect.signature (in 3.8 it emits the
deprecation warning based on kwargs)

* json: update whitelists

tests/stubtest_whitelists/py35.txt

@@ -36,6 +36,10 @@ io.BufferedRandom.read1
 io.BufferedReader.read1
 io.StringIO.readline
 ipaddress._BaseNetwork.__init__
+json.dump
+json.dumps
+json.load
+json.loads
 macpath.basename
 macpath.commonpath
 macpath.commonprefix

tests/stubtest_whitelists/py36.txt

@@ -39,10 +39,6 @@ io.BufferedRandom.read1
 io.BufferedReader.read1
 io.StringIO.readline
 ipaddress._BaseNetwork.__init__
-json.dump
-json.dumps
-json.load
-json.loads
 logging.handlers.MemoryHandler.__init__
 macpath.basename
 macpath.commonpath

tests/stubtest_whitelists/py37.txt

@@ -55,10 +55,6 @@ http.client.HTTPSConnection.__init__
 http.server.SimpleHTTPRequestHandler.__init__
 importlib.metadata
 ipaddress._BaseNetwork.__init__
-json.dump
-json.dumps
-json.load
-json.loads
 logging.handlers.MemoryHandler.__init__
 macpath.basename
 macpath.commonpath

tests/stubtest_whitelists/py38.txt

@@ -123,10 +123,6 @@ ipaddress.IPv6Interface.hostmask
 ipaddress._BaseNetwork.broadcast_address
 ipaddress._BaseNetwork.hostmask
 itertools.tee
-json.dump
-json.dumps
-json.load
-json.loads
 logging.handlers.MemoryHandler.__init__
 lzma.LZMACompressor.compress
 lzma.is_check_supported