go.tools/go/types: fix incorrect receiver in (*Selection).Type().
go.tools/go/types: fix incorrect receiver in (*Selection).Type().

Method expressions T.f are reported as having type (T)func(T),
i.e. T appears twice, as a receiver and a regular parameter.

LGTM=gri
R=gri
CC=golang-codereviews
https://codereview.appspot.com/96780044

t-yuki/go.tools.old,t-yuki/go.tools.old,t-yuki/go.tools.old