`ChainSupport` is an union of `deliver.support`, `broadcast.support`
and `ConsenterSupport`. Commit 16e170 introduced `SharedConfig` into
`deliver.support`, which conflicts with that in `ConsenterSupport`.
Due to Golang limitation https://github.com/golang/go/issues/6978

,
these methods are explicitly declared. However, `SharedConfig` was
removed in commit 6c28c8, which makes a clean interface viable again.

Also, a grammar error of a comment due to copy-paste is fixed.

Change-Id: I4cf3e78a28955226a150efda9cb539c28619771b
Signed-off-by: Jay Guo <guojiannan1101@gmail.com>