Redundant indexes in SQL Server
In general you should be able to remove Index2 without any major issues.  Index1 can cover any queries that Index2 would currently be handling (assuming there aren't any included column differences between the two).

If column C in Index1 is large, you might end up reading slightly more data into memory with Index1 for queries that would have used Index2 since that third column is taking up more space on each page, but in most scenarios I don't think you would notice any perceptible differences in performance.