refactor: replace golang.org/x/exp/slices with slices (#16772)

The experimental functions in `golang.org/x/exp/slices` are now
available in the standard library since Go 1.21.

Reference: https://go.dev/doc/go1.21#slices

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

coderd/database/dbmem/dbmem.go

@@ -10,6 +10,7 @@ import (
 	"math"
 	"reflect"
 	"regexp"
+	"slices"
 	"sort"
 	"strings"
 	"sync"
@@ -19,7 +20,6 @@ import (
 	"github.com/lib/pq"
 	"golang.org/x/exp/constraints"
 	"golang.org/x/exp/maps"
-	"golang.org/x/exp/slices"
 	"golang.org/x/xerrors"
 
 	"github.com/coder/coder/v2/coderd/notifications/types"