gdb: gdbarch.py: remove Info.__init__

gdb: gdbarch.py: remove Info.__init__

Info.__init__ currently assigns `self.predicate = None`.  This was
helpful to ensure that all component types had a `predicate` attribute.
The generator code could then avoid having code like "if the component
is anything but Info, use predicate".  Since the previous commit, all
component types have a predicate attribute which defaults to False.  We
can therefore remove the assignment in Info.__init__, and in turn remove
Info.__init__.  We however need to make the printer parameter of
_Component.__init__ optional, as Info don't need a printer.

Change-Id: I611edeca9cc9837eb49dddfe038595e1ff3b7239
Reviewed-By: Andrew Burgess <aburgess@redhat.com>