libct/cap: rm mapKeys, use maps.Keys, slices.Sorted

Since we've switched to Go 1.23 we can now use the new functionality of
maps and slices packages.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/capabilities/capabilities.go

@@ -5,7 +5,8 @@ package capabilities
 import (
 	"errors"
 	"fmt"
-	"sort"
+	"maps"
+	"slices"
 	"strings"
 	"sync"
 	"syscall"
@@ -67,7 +68,7 @@ func New(capConfig *configs.Capabilities) (*Caps, error) {
 		return nil, err
 	}
 	if len(unknownCaps) > 0 {
-		logrus.Warn("ignoring unknown or unavailable capabilities: ", mapKeys(unknownCaps))
+		logrus.Warn("ignoring unknown or unavailable capabilities: ", slices.Sorted(maps.Keys(unknownCaps)))
 	}
 	return &c, nil
 }
@@ -88,16 +89,6 @@ func capSlice(caps []string, unknownCaps map[string]struct{}) []capability.Cap {
 	return out
 }
 
-// mapKeys returns the keys of input in sorted order
-func mapKeys(input map[string]struct{}) []string {
-	keys := make([]string, 0, len(input))
-	for c := range input {
-		keys = append(keys, c)
-	}
-	sort.Strings(keys)
-	return keys
-}
-
 // Caps holds the capabilities for a container.
 type Caps struct {
 	pid  capability.Capabilities