[dynamo] Remove SuperSource (#110475)
The motivation for removing this is already present in the pre-PR comments. Copying it
~~~
# NB - SuperSource is a weird one.
# it is our only source with 2 bases, so we use the objec
# as the base, rather than the type, since an invocation
# like super(Foo, foo) is represented here, the source object base is more spiritually
# aligned with the instance, rather than the type.
# This whole construction is questionable tho, and we should probably find a way to
# avoid this exception to our otherwise nice source parentage invariant.
~~~
Instead of using super(a, b), we can use `type(b).__mro__[index]`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/110475
Approved by: https://github.com/jansel
