errors/fmt: re-enable TestPanics test on builders

The test has been fixed in CL 204078, so there isn't a need
to skip it on builders anymore.

Updates golang/go#30622

Change-Id: I88aeed35f963a9cdfe9b5ee6241956d23c2d23ad
Reviewed-on: https://go-review.googlesource.com/c/exp/+/204140
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: dmitshur

errors/fmt/fmt_test.go

@@ -9,7 +9,6 @@ import (
 	. "fmt"
 	"io"
 	"math"
-	"os"
 	"reflect"
 	"runtime"
 	"strings"
@@ -1685,9 +1684,6 @@ var stripMethod = strings.NewReplacer(
 )
 
 func TestPanics(t *testing.T) {
-	if os.Getenv("GO_BUILDER_NAME") != "" {
-		t.Skipf("skipping broken test on builders; see https://golang.org/issue/30622")
-	}
 	for i, tt := range panictests {
 		s := Sprintf(tt.fmt, tt.in)
 		s = stripMethod.Replace(s)