Remove Python 3.4 support (#3147)

Closes #3123

third_party/3/contextvars.pyi

@@ -0,0 +1,30 @@
+from typing import Any, Callable, ClassVar, Generic, Iterator, Mapping, TypeVar, Union
+
+_T = TypeVar('_T')
+
+class ContextVar(Generic[_T]):
+    def __init__(self, name: str, *, default: _T = ...) -> None: ...
+    @property
+    def name(self) -> str: ...
+    def get(self, default: _T = ...) -> _T: ...
+    def set(self, value: _T) -> Token[_T]: ...
+    def reset(self, token: Token[_T]) -> None: ...
+
+class Token(Generic[_T]):
+    @property
+    def var(self) -> ContextVar[_T]: ...
+    @property
+    def old_value(self) -> Any: ...  # returns either _T or MISSING, but that's hard to express
+    MISSING: ClassVar[object]
+
+def copy_context() -> Context: ...
+
+# It doesn't make sense to make this generic, because for most Contexts each ContextVar will have
+# a different value.
+class Context(Mapping[ContextVar[Any], Any]):
+    def __init__(self) -> None: ...
+    def run(self, callable: Callable[..., _T], *args: Any, **kwargs: Any) -> _T: ...
+    def copy(self) -> Context: ...
+    def __getitem__(self, key: ContextVar[Any]) -> Any: ...
+    def __iter__(self) -> Iterator[ContextVar[Any]]: ...
+    def __len__(self) -> int: ...

third_party/3/pkg_resources/py31compat.pyi

@@ -4,11 +4,4 @@ import sys
 
 needs_makedirs: bool
 
-def _makedirs_31(path: Text, exist_ok: bool = ...) -> None: ...
-
-# _makedirs_31 has special behavior to handle an edge case that was removed in
-# 3.4.1. No one should be using 3.4 instead of 3.4.1, so this should be fine.
-if sys.version_info >= (3,):
-    makedirs = os.makedirs
-else:
-    makedirs = _makedirs_31
+makedirs = os.makedirs