crypto/tls: small bogo shim test tidying

1. onResumeShimWritesFirst is unused, replace the binding with an
   underscore.
2. in the bogoShim() function when looping through resumeCount+1 the
   tlsConn read for loop only breaks for non-nil err, so there's no need
   to check that again after the loop body.

Updates #72006

Change-Id: Ieff45d26df33d71003a2509ea5b2b06c5fa0e1d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/650715
Reviewed-by: Roland Shoemaker <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

Author: cpu

Diff for: src/crypto/tls/bogo_shim_test.go

@@ -82,10 +82,10 @@ var (
 
 	expectSessionMiss = flag.Bool("expect-session-miss", false, "")
 
-	_                       = flag.Bool("enable-early-data", false, "")
-	_                       = flag.Bool("on-resume-expect-accept-early-data", false, "")
-	_                       = flag.Bool("expect-ticket-supports-early-data", false, "")
-	onResumeShimWritesFirst = flag.Bool("on-resume-shim-writes-first", false, "")
+	_ = flag.Bool("enable-early-data", false, "")
+	_ = flag.Bool("on-resume-expect-accept-early-data", false, "")
+	_ = flag.Bool("expect-ticket-supports-early-data", false, "")
+	_ = flag.Bool("on-resume-shim-writes-first", false, "")
 
 	advertiseALPN        = flag.String("advertise-alpn", "", "")
 	expectALPN           = flag.String("expect-alpn", "", "")
@@ -324,7 +324,7 @@ func bogoShim() {
 				break
 			}
 		}
-		if err != nil && err != io.EOF {
+		if err != io.EOF {
 			retryErr, ok := err.(*ECHRejectionError)
 			if !ok {
 				log.Fatalf("unexpected error type returned: %v", err)