Dear Krishna.
You can maintain field selection here.
IMG -> Financial Supply Chain Management -> Treasury and Risk Management -> Transaction Manager -> Securities -> Master Data -> Securities Account Management -> Maintain Field Selection for Security Account Master Data (tr. S_ALR_87004253)
but you will not find Depositary bank field there. You can Suppress all fields, but Depositary bank field will remain.
I think it's because of logic about Securities Account. If you have Securities Account then it must be situated somewhere in Depositary bank. That's why this field has Required Entry status.