remove u.eig, v.eig and wa.eig items from cca.default

The cca.object was documented in vegan 1.6-10 (Sep 26, 2005), and
in that document we warn that there is "no guarantee" that these
itmems will be kept in future release. In commit bddfea39 (Mar 5, 2013)
we use harsher tone and said that the "item will be removed". However,
that harsher text has not been in any release version so that this
may be an abrupt change.
remove u.eig etc from rda
remove v.eig item from capscale result

wa.eig and u.eig already disappeared with rda changes.

The result still has CA$imaginary.u.eig (scaled scores for
imaginary axes). These are the only scores returned for
imaginary axes.
neither ade2vegancca returns u.eig, v.eig, wa.eig
man/cca.object.Rd updated to new cca object without .eig scores

There is a note about changes which here are suggested to be
effective in vegan 2.2-0.
man/cca.object tells about imaginary.u.eig scores in capscale
Merge pull request #51 from jarioksa/remove-u.eig-etc

Remove u.eig etc