mantle/kola: remove rand.Seed()

This is to appease golangci-lint:

```
Error: SA1019: rand.Seed has been deprecated since Go 1.20 and an alternative
has been available since Go 1.0: As of Go 1.20 there is no reason to call Seed
with a random value. Programs that call Seed with a known value to get a
specific sequence of results should use New(NewSource(seed)) to obtain a local
random generator.  (staticcheck)
```

According to https://pkg.go.dev/math/rand#Seed "If Seed is not called, the
generator is seeded randomly at program startup." so I think it's safe to
just drop it.

mantle/cmd/kola/kola.go

@@ -17,15 +17,13 @@ package main
 import (
 	"encoding/json"
 	"fmt"
-	"math/rand"
 	"net/http"
 	"os"
 	"path/filepath"
 	"regexp"
 	"sort"
 	"strings"
 	"text/tabwriter"
-	"time"
 
 	"github.com/coreos/pkg/capnslog"
 	"github.com/pkg/errors"
@@ -160,8 +158,6 @@ func init() {
 }
 
 func main() {
-	// initialize global state
-	rand.Seed(time.Now().UnixNano())
 	cli.Execute(root)
 }