Redundant blank argument in range

Reports optional blank variables in range loops.

When you use the range loop to iterate over a slice, two values are returned for each iteration. The first is the index number, and the second is a copy of the element at that index. If you do not need the second value, you can skip this element instead of using a blank identifier.

Example:

for a, _ = range v {} // `for a, _ =` is the same as `for a =`

To remove the blank identifier, you can use the Delete blank argument quick-fix. After the quick-fix is applied, the code will look as follows:

for a = range v {}