Remove specail casing in Execute()

We had some stuff that created a new empty []string if args was already
and empty string (why?)

We had some stuff that called Help() if it wasn't runnable (but
.execute() already does that)

Just remove the special case stuff.

command.go

@@ -476,21 +476,10 @@ func (c *Command) Execute() (err error) {
 		args = c.args
 	}
 
-	if len(args) == 0 {
-		// Only the executable is called and the root is runnable, run it
-		if c.Runnable() {
-			err = c.execute([]string(nil))
-		} else {
-			c.Help()
-		}
-	} else {
-		cmd, flags, e := c.Find(args)
-		if e != nil {
-			err = e
-		} else {
+	cmd, flags, err := c.Find(args)
+	if err == nil {
 		err = cmd.execute(flags)
 	}
-	}
 
 	if err != nil {
 		if err == flag.ErrHelp {