There is no need to inform the remaining school of your intentions. Your deposit says enough.
If you are a sufficiently special snowflake that merit scholarships are a possibility, then yes, withdrawing from backup contenders may make a difference in what you are offered.
If you are a sufficiently special snowflake that merit scholarships are a possibility, then yes, withdrawing from backup contenders may make a difference in what you are offered.
To clarify, by holding multiple acceptances as long as the traffic rules for applicants allows (generally mid-May) leads to the school you are matriculating to the chance to actually see that you are accepted elsewhere. Generally, they are made aware of your multiple acceptances mid-Spring. If you are this special snowflake (which is exceedingly unlikely for the vast, vast majority of applicants even with stellar stats and ECs) and they just have to have you, this could cause them to entice you to attend using a merit scholarship.
This is why many high caliber applicants defer making decisions until after they receive their financial aid packages from each school.
As for notification, Cat is correct in that your deposit is the ticket. Congratulations!