How to Modify Convert To Case System Dialog in CRM2013 onPremise

Hi ,

I have requirement to remove Subject Control from dialog as shown below but i can see in 

 server Under  directory path CRMWeb\Activities\act_dlgs which  being called here .but control associated with Subject control is of type SDK:Lookupcontrol ,If i try to remove/hide this control on this act_dlgs.aspx page system gives error.

Can you please advise me how can i can i remove this Subject control from dialog by keeping other functionality intact.

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