Address `go vet` and `saticcheck` issues

Run `go mod tidy`

Resolve staticcheck issues:
- SA2002 `t.Fatal`  must be called in the same goroutine as the test
- U1000 unused struct
- ST1005 error string should not be capitalized

The `go vet` issues were the same as the ones reported by `saticcheck`.

Relates to:
- https://github.com/orgs/ipfs/projects/12#card-58209321

p2p/transport/testsuite/stream_suite.go

@@ -158,7 +158,7 @@ func goServe(t *testing.T, l transport.Listener) (done func()) {
 
 func SubtestStress(t *testing.T, ta, tb transport.Transport, maddr ma.Multiaddr, peerA peer.ID, opt Options) {
 	msgsize := 1 << 11
-	errs := make(chan error, 0) // dont block anything.
+	errs := make(chan error) // dont block anything.
 
 	rateLimitN := 5000 // max of 5k funcs, because -race has 8k max.
 	rateLimitChan := make(chan struct{}, rateLimitN)
@@ -211,7 +211,7 @@ func SubtestStress(t *testing.T, ta, tb transport.Transport, maddr ma.Multiaddr,
 
 		s, err := c.OpenStream(context.Background())
 		if err != nil {
-			errs <- fmt.Errorf("Failed to create NewStream: %s", err)
+			errs <- fmt.Errorf("failed to create NewStream: %s", err)
 			return
 		}
 

p2p/transport/testsuite/transport_suite.go

@@ -8,7 +8,6 @@ import (
 	"sync"
 	"testing"
 
-	"github.com/libp2p/go-libp2p-core/mux"
 	"github.com/libp2p/go-libp2p-core/peer"
 	"github.com/libp2p/go-libp2p-core/transport"
 
@@ -17,11 +16,6 @@ import (
 
 var testData = []byte("this is some test data")
 
-type streamAndConn struct {
-	stream mux.MuxedStream
-	conn   transport.CapableConn
-}
-
 func SubtestProtocols(t *testing.T, ta, tb transport.Transport, maddr ma.Multiaddr, peerA peer.ID) {
 	rawIPAddr, _ := ma.NewMultiaddr("/ip4/1.2.3.4")
 	if ta.CanDial(rawIPAddr) || tb.CanDial(rawIPAddr) {
@@ -271,7 +265,7 @@ func SubtestPingPong(t *testing.T, ta, tb transport.Transport, maddr ma.Multiadd
 				return
 			}
 			if err = s.CloseWrite(); err != nil {
-				t.Fatal(err)
+				t.Error(err)
 				return
 			}
 
@@ -286,7 +280,7 @@ func SubtestPingPong(t *testing.T, ta, tb transport.Transport, maddr ma.Multiadd
 			}
 
 			if err = s.Close(); err != nil {
-				t.Fatal(err)
+				t.Error(err)
 				return
 			}
 		}(i)