Cleanup

unless the constants are needed, this would be better as a simple table.

```
var units = ["B", "KB", "MB", ...]
```
then
```
mult, unit := 1, units[0]
for _, u := range units[1:] {
  if b>>10 < u {
    unit = u
    break
  }
  mult <<= 10
}
return fmt.Sprintf("%.2f%s", float64(b)/float64(mult), unit)
```

or something like that.