Remove tuple's __init__ method (#2467)

The __new__ method should suffice, and having both interferes with providing
a __new__ in namedtuples, which we want to do to fix
python/mypy#1279.

Author: msullivan

stdlib/2/__builtin__.pyi

@@ -517,7 +517,6 @@ class slice(object):
 
 class tuple(Sequence[_T_co], Generic[_T_co]):
     def __new__(cls: Type[_T], iterable: Iterable[_T_co] = ...) -> _T: ...
-    def __init__(self, iterable: Iterable[_T_co] = ...) -> None: ...
     def __len__(self) -> int: ...
     def __contains__(self, x: object) -> bool: ...
     @overload

stdlib/2/builtins.pyi

@@ -517,7 +517,6 @@ class slice(object):
 
 class tuple(Sequence[_T_co], Generic[_T_co]):
     def __new__(cls: Type[_T], iterable: Iterable[_T_co] = ...) -> _T: ...
-    def __init__(self, iterable: Iterable[_T_co] = ...) -> None: ...
     def __len__(self) -> int: ...
     def __contains__(self, x: object) -> bool: ...
     @overload

stdlib/3/builtins.pyi

@@ -559,7 +559,6 @@ class slice:
 
 class tuple(Sequence[_T_co], Generic[_T_co]):
     def __new__(cls: Type[_T], iterable: Iterable[_T_co] = ...) -> _T: ...
-    def __init__(self, iterable: Iterable[_T_co] = ...) -> None: ...
     def __len__(self) -> int: ...
     def __contains__(self, x: object) -> bool: ...
     @overload