cache: Remove mutex support as it is not needed

No one uses the mutex in cache object so it can be removed.
Can be reintroduced if fine grained locking is needed there.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

pkg/resmgr/cache/cache.go

@@ -21,7 +21,6 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"sync"
 
 	nri "github.com/containerd/nri/pkg/api"
 	v1 "k8s.io/api/core/v1"
@@ -435,8 +434,7 @@ var (
 
 // Our cache of objects.
 type cache struct {
-	sync.Mutex `json:"-"` // we're lockable
-	dataDir    string     // container data directory
+	dataDir string // container data directory
 
 	Pods       map[string]*pod       // known/cached pods
 	Containers map[string]*container // known/cache containers