library/machine.Pin: Remove .id() method and .board class attr.

Both aren't part of generic Hardware API: It's impossible to implement
.id() method in a generic case (e.g., when Pin is instantiated by the
underlying OS/RTOS). .board attribute is an obvious space hog which
instead can be implemented on Python level if needed.

docs/library/machine.Pin.rst

@@ -158,11 +158,6 @@ Methods
    and get the value of the pin.  It is equivalent to Pin.value([x]).
    See :meth:`Pin.value` for more details.
 
-.. method:: Pin.id()
-
-   Get the pin identifier.  This may return the ``id`` as specified in the
-   constructor.  Or it may return a canonical software-specific pin id.
-
 .. method:: Pin.mode([mode])
 
    Get or set the pin mode.
@@ -217,19 +212,6 @@ Methods
 
    This method returns a callback object.
 
-Attributes
-----------
-
-.. class:: Pin.board
-
-    Contains all ``Pin`` objects supported by the board. Examples::
-
-        Pin.board.GP25
-        led = Pin(Pin.board.GP25, mode=Pin.OUT)
-        Pin.board.GP2.alt_list()
-
-    Availability: WiPy.
-
 Constants
 ---------