cmd/screentest: remove special case for same URL

The special case added in a previous CL is not the problem.
In general, waiting for components to render is a better solution.

Change-Id: Iadecccea7862db0cbfcfc525392b8859b78dda6d
Reviewed-on: https://go-review.googlesource.com/c/website/+/628055
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

cmd/golangorg/testdata/screentest/relnotes.txt

@@ -7,5 +7,8 @@ capture fullscreen
 {{range ints 1 22}}
   test rl{{.}}
   path /doc/go1.{{.}}
+  # dd.indent is added by one of the last bits of JS to run on the page:
+  # generateTOC in https://go.dev/js/godocs.js.
+  wait dd.indent
   capture fullscreen
 {{end}}

cmd/screentest/screentest.go

@@ -13,7 +13,6 @@ package main
 import (
 	"bufio"
 	"bytes"
-	"cmp"
 	"context"
 	"errors"
 	"fmt"
@@ -485,17 +484,6 @@ func (tc *testcase) run(ctx context.Context, update bool) (err error) {
 	fmt.Fprintf(&tc.output, "test %s ", tc.name)
 	var testScreen, wantScreen image.Image
 	g, ctx := errgroup.WithContext(ctx)
-	// If the hosts are the same, chrome (or chromedp) does not handle concurrent requests well.
-	// This wouldn't make sense in an actual test, but it does happen in this package's tests.
-	urla, erra := url.Parse(tc.testURL)
-	urlb, errb := url.Parse(tc.wantURL)
-	if err := cmp.Or(erra, errb); err != nil {
-		return err
-	}
-	if urla.Host == urlb.Host {
-		g.SetLimit(1)
-	}
-
 	g.Go(func() error {
 		testScreen, err = tc.screenshot(ctx, tc.testURL, tc.testPath, tc.testImageReader)
 		return err