Unique constraint on multiple columns and one of them already has index
If the purpose of the unique constraint (with its associated unique index) is simply to enforce uniqueness then you should change the column order for your unique constraint to col3, col4, col1, col2 and then your index will be redundant and can be dropped.

Otherwise there may be some benefit from having another index on your table with different leading columns, you should consider your workload, if the table is often accessed with a predicate on col1 or on both col1 and col2 and maybe that is a good case to have those columns first in the key.

Also @srutzky comment about the clustered index has merit and is worth considering.