merge 2 and 3 stubs for fileinput (#1319)

* merge 2 and 3 stubs for fileinput

Plus some minor fixes.

* pytype doesn't like generic type aliases

stdlib/2/fileinput.pyi

@@ -1,46 +0,0 @@
-from typing import Iterable, Callable, IO, Optional, Union, Iterator
-
-class FileInput(Iterable[str]):
-    def __init__(
-        self,
-        files: Optional[Union[str, Iterable[str]]] = None,
-        inplace: bool = ...,
-        backup: str = ...,
-        bufsize: int = ...,
-        mode: str = ...,
-        openhook: Callable[[str, str], IO[str]] = ...
-    ) -> None: ...
-
-    def __del__(self) -> None: ...
-    def close(self) -> None: ...
-    def __iter__(self) -> Iterator[str]: ...
-    def __getitem__(self, i: Union[int, slice]) -> str: ...
-    def next(self) -> str: ...
-    def nextfile(self) -> None: ...
-    def readline(self) -> str: ...
-    def filename(self) -> Optional[str]: ...
-    def lineno(self) -> int: ...
-    def filelineno(self) -> int: ...
-    def fileno(self) -> int: ...
-    def isfirstline(self) -> bool: ...
-    def isstdin(self) -> bool: ...
-
-def input(
-    files: Optional[Union[str, Iterable[str]]] = None,
-    inplace: bool = ...,
-    backup: str = ...,
-    bufsize: int = ...,
-    mode: str = ...,
-    openhook: Callable[[str, str], IO[str]] = ...) -> FileInput: ...
-
-
-def filename() -> Optional[str]: ...
-def lineno() -> int: ...
-def filelineno() -> int: ...
-def isfirstline() -> bool: ...
-def isstdin() -> bool: ...
-def nextfile() -> None: ...
-def close() -> None: ...
-
-def hook_compressed(filename: str, mode: str) -> IO[str]: ...
-def hook_encoded(encoding: str) -> Callable[[str, str], IO[str]]: ...