cmd/go/internal: use the newly added strings.CutSuffix method to optimize the code

Signed-off-by: cui fliter <imcusg@gmail.com>

src/cmd/go/internal/clean/clean.go

@@ -340,16 +340,14 @@ func clean(p *load.Package) {
 			continue
 		}
 
-		if strings.HasSuffix(name, "_test.go") {
-			base := name[:len(name)-len("_test.go")]
+		if base, found := strings.CutSuffix(name, "_test.go"); found {
 			allRemove = append(allRemove, base+".test", base+".test.exe")
 		}
 
-		if strings.HasSuffix(name, ".go") {
+		if base, found := strings.CutSuffix(name, ".go"); found {
 			// TODO(adg,rsc): check that this .go file is actually
 			// in "package main", and therefore capable of building
 			// to an executable file.
-			base := name[:len(name)-len(".go")]
 			allRemove = append(allRemove, base, base+".exe")
 		}
 	}

src/cmd/go/internal/load/pkg.go

@@ -3115,10 +3115,10 @@ func PackagesAndErrorsOutsideModule(ctx context.Context, opts PackageOpts, args
 	}
 	patterns := make([]string, len(args))
 	for i, arg := range args {
-		if !strings.HasSuffix(arg, "@"+version) {
+		p, found := strings.CutSuffix(arg, "@"+version)
+		if !found {
 			return nil, fmt.Errorf("%s: all arguments must refer to packages in the same module at the same version (@%s)", arg, version)
 		}
-		p := arg[:len(arg)-len(version)-1]
 		switch {
 		case build.IsLocalImport(p):
 			return nil, fmt.Errorf("%s: argument must be a package path, not a relative path", arg)