MB-10282: Remove Connection class

The Connection class contained data for a particular connection,
but since the ConnHandler class just contains accessors for the
almost all of the Connection classes data we should just merge
the two classes together.

Change-Id: Ie03174873e2969cb154f229d10086b0058c5e9dc
Reviewed-on: http://review.couchbase.org/33913
Tested-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>