[CA-128364] & [CP-7396]: Fix tapdisk rrd plugin deregister call.

Signed-off-by: Siddharth Vinothkumar <siddharth.vinothkumar@citrix.com>
Reviewed-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>

GitHub: closes #88 on xapi-project/sm