Arrays don’t have a RemoveAt() method. Also, your code uses square brackes instead of parentheses (), which is used for accessing an array rather than calling a method.
It seems like you’re wanting something like a C# List in Javascript. To do this:
import System.Collections.Generic; //this import lets this file access the definition of what a List is, amongst other types found under generic collections
var gameObjectList : List.<GameObject> = new List.<GameObject>();
function Update() {
if (Input.GetAxis("Jump")) {
gameObjectList.RemoveAt(0); //0 will remove the first object, which I'm assuming is what you really wanted ;)
}
}