Remove Main reference from IdentityManager.

(There's nothing particularly wrong with this, but it keeps showing
up when I try to find usages of Main to remove.)

Change-Id: I291ca91fc7e80e9dab40befa31424d9d7e0b62d1
Reviewed-on: http://gerrit.dmdirc.com/2665
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager