Remove all darwin specific files and use more generic _unsupported with build tags.

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)

mount/mounter_unsupported.go

@@ -0,0 +1,10 @@
+// +build: !linux !amd64
+package mount
+
+func mount(device, target, mType string, flag uintptr, data string) error {
+	panic("Not implemented")
+}
+
+func unmount(target string, flag int) error {
+	panic("Not implemented")
+}