refactor: remove misleading comment

Remove comment that is misleading.  As stated in the doc comment, a
solution may not be found in the pathological case, in which case
`ProgramError` would be returned.

Author: yancyribbens

src/single_random_draw.rs

@@ -102,9 +102,6 @@ pub fn single_random_draw<
     if max_tx_weight_exceeded {
         Err(MaxWeightExceeded)
     } else {
-        // This should never be reached.
-        // Either there is not enough funds, or an overflow occurred.
-        // If neither of those two things occurred, then a solution should be found.
         Err(ProgramError)
     }
 }