clean python 3 specific stuff from stdlib/@python2 stubs (#5451)

stdlib/@python2/ensurepip/__init__.pyi

@@ -2,24 +2,11 @@ import sys
 from typing import Optional
 
 def version() -> str: ...
-
-if sys.version_info >= (3, 0):
-    def bootstrap(
-        *,
-        root: Optional[str] = ...,
-        upgrade: bool = ...,
-        user: bool = ...,
-        altinstall: bool = ...,
-        default_pip: bool = ...,
-        verbosity: int = ...,
-    ) -> None: ...
-
-else:
-    def bootstrap(
-        root: Optional[str] = ...,
-        upgrade: bool = ...,
-        user: bool = ...,
-        altinstall: bool = ...,
-        default_pip: bool = ...,
-        verbosity: int = ...,
-    ) -> None: ...
+def bootstrap(
+    root: Optional[str] = ...,
+    upgrade: bool = ...,
+    user: bool = ...,
+    altinstall: bool = ...,
+    default_pip: bool = ...,
+    verbosity: int = ...,
+) -> None: ...