MB-10127 Remove dead code.

Change-Id: I2b168cea4701fd89297abfbc1e696203fb08b65e
Reviewed-on: http://review.couchbase.org/33423
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-10127 Eliminate xdc_vbucket_rep_xmem_{srv,worker} modules.

In order to avoid the state and messages to these processes being
logged in case of permanent problems on the remote memcached. Which,
we know, may blow up error_logger's memory usage.

And there was only one xmem_worker anyway. Every memcached request
would first go through xmem_srv to xmem_worker. So I converted
xmem_worker into a library which is used in place of old calls to
xmem_srv.

Change-Id: Ie308e3de1439e88edae261ca71e4036be36fb393
Reviewed-on: http://review.couchbase.org/33424
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>