ipsec: Remove unit tests for xfrm_collector

Remove the unit tests for xfrm_collector. They are simply not worth it.
All xfrm_collector does is collect statistics via helper functions and
feed them into Prometheus functions. The helper functions are covered by
unit tests. Prometheus functions are covered by unit tests. We're really
just passing the information from one to the other.

But to cover this trivial logic in unit tests, we end up copying lots of
information across the code and tests. We also need to pass the helper
functions as a function pointer to xfrm_collector. Every new metric is
going to need a new function pointer.

I believe this is a waste of engineering time and very unlikely to catch
mistakes. It doesn't even test the helper functions since we mock them
out. So it's really unclear what we're trying to cover here. Removing it
makes it easier to add new metrics in followup commits.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>

pkg/datapath/linux/ipsec/xfrm_collector.go

@@ -37,22 +37,12 @@ const (
 )
 
 type xfrmCollector struct {
-	xfrmStatFunc func() (procfs.XfrmStat, error)
-
 	// Inbound errors
 	xfrmErrorDesc *prometheus.Desc
 }
 
-// NewXFRMCollector returns a new prometheus.Collector for /proc/net/xfrm_stat
-// https://www.kernel.org/doc/Documentation/networking/xfrm_proc.txt
 func NewXFRMCollector() prometheus.Collector {
-	return newXFRMCollector(procfs.NewXfrmStat)
-}
-
-func newXFRMCollector(statFn func() (procfs.XfrmStat, error)) prometheus.Collector {
 	return &xfrmCollector{
-		xfrmStatFunc: statFn,
-
 		xfrmErrorDesc: prometheus.NewDesc(
 			prometheus.BuildFQName(metrics.Namespace, subsystem, "xfrm_error"),
 			"Total number of xfrm errors",
@@ -66,7 +56,7 @@ func (x *xfrmCollector) Describe(ch chan<- *prometheus.Desc) {
 }
 
 func (x *xfrmCollector) Collect(ch chan<- prometheus.Metric) {
-	stats, err := x.xfrmStatFunc()
+	stats, err := procfs.NewXfrmStat()
 	if err != nil {
 		log.WithError(err).Error("Error while getting xfrm stats")
 		return