Revert "hit/miss stats for matchcache"

This reverts commit 3bae47f.

They consume about 1% cpu (flat and cumul) under heavy ingest load
and they basically just confirm it works exactly like it should.

But the commit is here in case someone ever wants to re-apply it.

mdata/init.go

@@ -91,6 +91,6 @@ func ConfigProcess() {
 }
 
 func Cache(cleanInterval, expireAfter time.Duration) {
-	schemasCache = matchcache.New("schemas", cleanInterval, expireAfter)
-	aggsCache = matchcache.New("aggs", cleanInterval, expireAfter)
+	schemasCache = matchcache.New(cleanInterval, expireAfter)
+	aggsCache = matchcache.New(cleanInterval, expireAfter)
 }

mdata/matchcache/matchcache.go

@@ -1,11 +1,8 @@
 package matchcache
 
 import (
-	"fmt"
 	"sync"
 	"time"
-
-	"github.com/raintank/metrictank/stats"
 )
 
 // Cache caches key to uint16 lookups (for schemas and aggregations)
@@ -18,22 +15,18 @@ type Cache struct {
 
 	cleanInterval time.Duration
 	expireAfter   time.Duration
-	hits          *stats.Counter32
-	miss          *stats.Counter32
 }
 
 type Item struct {
 	val  uint16
 	seen int64
 }
 
-func New(name string, cleanInterval, expireAfter time.Duration) *Cache {
+func New(cleanInterval, expireAfter time.Duration) *Cache {
 	m := &Cache{
 		data:          make(map[string]Item),
 		cleanInterval: cleanInterval,
 		expireAfter:   expireAfter,
-		hits:          stats.NewCounter32(fmt.Sprintf("idx.matchcache.%s.ops.hit", name)),
-		miss:          stats.NewCounter32(fmt.Sprintf("idx.matchcache.%s.ops.miss", name)),
 	}
 	go m.maintain()
 	return m
@@ -45,10 +38,7 @@ type AddFunc func(key string) uint16
 func (m *Cache) Get(key string, fn AddFunc) uint16 {
 	m.Lock()
 	item, ok := m.data[key]
-	if ok {
-		m.hits.Inc()
-	} else {
-		m.miss.Inc()
+	if !ok {
 		item.val = fn(key)
 	}
 	item.seen = time.Now().Unix()