Delete accumulate problem. Fixes #18.
Delete accumulate problem. Fixes #18.

For now I'm leaving the actual files in place, but they will only be
served to someone who is using the `exercism restore` command.

Once I verify that the `restore` command will work even if completed
exercises are missing, I'll delete the problem files as well.

pminten/xgo,leenipper/xgo,leenipper/xgo,robphoenix/exercism-go,exercism/xgo,robphoenix/exercism-go,pminten/xgo,exercism/xgo