chore(ur): move structs to reduce dependency chain

lib/ur brings in a lot of dependencies we don't need in e.g.
stcrashreceiver, who only needs the small failure reporting structs.
Make those part of the lean `contract` package instead.

Signed-off-by: Jakob Borg <jakob@kastelo.net>

lib/ur/contract/contract.go

@@ -282,3 +282,16 @@ func clear(v interface{}, since int) error {
 	}
 	return nil
 }
+
+type FailureReport struct {
+	FailureData
+
+	Count   int
+	Version string
+}
+
+type FailureData struct {
+	Description string
+	Goroutines  string
+	Extra       map[string]string
+}