Drop support for Python 3.5 (#4675)

Python 3.5 EOL was on 2020-09-30.

stdlib/3/urllib/request.pyi

@@ -1,6 +1,5 @@
 import os
 import ssl
-import sys
 from email.message import Message
 from http.client import HTTPMessage, HTTPResponse, _HTTPConnectionProtocol
 from http.cookiejar import CookieJar
@@ -250,22 +249,12 @@ class HTTPErrorProcessor(BaseHandler):
     def http_response(self, request: Request, response: HTTPResponse) -> _UrlopenRet: ...
     def https_response(self, request: Request, response: HTTPResponse) -> _UrlopenRet: ...
 
-if sys.version_info >= (3, 6):
-    def urlretrieve(
-        url: str,
-        filename: Optional[Union[str, os.PathLike[Any]]] = ...,
-        reporthook: Optional[Callable[[int, int, int], None]] = ...,
-        data: Optional[bytes] = ...,
-    ) -> Tuple[str, HTTPMessage]: ...
-
-else:
-    def urlretrieve(
-        url: str,
-        filename: Optional[str] = ...,
-        reporthook: Optional[Callable[[int, int, int], None]] = ...,
-        data: Optional[bytes] = ...,
-    ) -> Tuple[str, HTTPMessage]: ...
-
+def urlretrieve(
+    url: str,
+    filename: Optional[Union[str, os.PathLike[Any]]] = ...,
+    reporthook: Optional[Callable[[int, int, int], None]] = ...,
+    data: Optional[bytes] = ...,
+) -> Tuple[str, HTTPMessage]: ...
 def urlcleanup() -> None: ...
 
 class URLopener:

stdlib/3/urllib/robotparser.pyi

@@ -13,8 +13,7 @@ class RobotFileParser:
     def can_fetch(self, user_agent: str, url: str) -> bool: ...
     def mtime(self) -> int: ...
     def modified(self) -> None: ...
-    if sys.version_info >= (3, 6):
-        def crawl_delay(self, useragent: str) -> Optional[str]: ...
-        def request_rate(self, useragent: str) -> Optional[_RequestRate]: ...
+    def crawl_delay(self, useragent: str) -> Optional[str]: ...
+    def request_rate(self, useragent: str) -> Optional[_RequestRate]: ...
     if sys.version_info >= (3, 8):
         def site_maps(self) -> Optional[List[str]]: ...