Use Go standard library slices package instead of x/exp/slices

The former is available since Go 1.21 and the latter is merely a wrapper
around it when using Go ≥ 1.21. Use the standard library package
directly.

We cannot yet switch out x/exp/maps for the standard library maps
package as the maps.Keys function used in statedb code base is only
available in Go ≥ 1.23.

Signed-off-by: Tobias Klauser <tobias@cilium.io>

reconciler/helpers.go

@@ -6,8 +6,7 @@ package reconciler
 import (
  "errors"
  "fmt"
-
- "golang.org/x/exp/slices"
+ "slices"
 )
 
 var closedWatchChannel = func() <-chan struct{} {