How to enable Single Company Login?

If the system administrator wishes to disable the company dropdown list from the login page in order not to allow the user to select another company to log in. 

<add key="IsSingleCompanyLogin" value="true"/> 


https://trial.hrpro.hk:8081/WebClient/Home/Login/?dbname=dbDemo2016
or 

https://trial.hrpro.hk:8081/WebClient/Home/Login/?dbname=dbYH0001