Context menu "Remove this argument (A)"
⚠️ Obsolete since IDA 7.5 has the same. Available when build with an older SDK
Sometimes Hex-Rays thinks that a register is used as an argument for a function but it isn't so. It was also tiresome to type "home, home, y, ctrl->right, ctrl-shift-right, delete, enter". So here is an easiest way to deal with it.
Just select that argument in the first line of pseudocode and choose "Remove this argument".