ec.c, field.c: Remove redundant `FOO_pyrichcompare' methods.

The abstract base classes already have the necessary comparison methods,
so there's nothing to be gained by repeating the same methods on
subclasses.  (Indeed, Python might pointlessly allocate more memory for
the corresponding Python-level descriptors, but I haven't checked.)  But
there is something to be lost: Python 3 explicitly clobbers the
`__hash__' methods of subclasses which declare new equality methods.  We
could add duplicates of the hash methods throughout the subclass graph,
but it seems better to delete the pointless equality methods which are
causing the problem.