program: allow delegate to update user position max margin ratio (#1913)

Author: crispheaney

programs/drift/src/instructions/user.rs

@@ -4448,14 +4448,9 @@ pub struct UpdateUser<'info> {
 }
 
 #[derive(Accounts)]
-#[instruction(
-    sub_account_id: u16,
-)]
 pub struct UpdateUserPerpPositionCustomMarginRatio<'info> {
     #[account(
         mut,
-        seeds = [b"user", authority.key.as_ref(), sub_account_id.to_le_bytes().as_ref()],
-        bump,
         constraint = can_sign_for_user(&user, &authority)?
     )]
     pub user: AccountLoader<'info, User>,