Add unused linter.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

cli/compose/loader/loader_test.go

@@ -632,10 +632,6 @@ func durationPtr(value time.Duration) *time.Duration {
 	return &value
 }
 
-func int64Ptr(value int64) *int64 {
-	return &value
-}
-
 func uint64Ptr(value uint64) *uint64 {
 	return &value
 }