refactor: replace Readdir(-1) with os.ReadDir (#3361)

We can simplify the following code
	dir, err := os.Open(dirname)
	if err != nil {
		return err
	}
	defer dir.Close()

	dirs, err := dir.Readdir(-1)

with just `os.ReadDir(dirname)`.

Reference: https://pkg.go.dev/os#ReadDir

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/proc/core/core_test.go

@@ -504,12 +504,7 @@ func procdump(t *testing.T, exePath string) string {
 		t.Fatalf("possible error running procdump64, output: %q, error: %v", string(out), err)
 	}
 
-	dh, err := os.Open(exeDir)
+	fis, err := os.ReadDir(exeDir)
-	if err != nil {
-		t.Fatalf("could not open executable file directory %q: %v", exeDir, err)
-	}
-	defer dh.Close()
-	fis, err := dh.Readdir(-1)
 	if err != nil {
 		t.Fatalf("could not read executable file directory %q: %v", exeDir, err)
 	}

pkg/proc/gdbserial/rr.go

@@ -300,12 +300,7 @@ func RecordAndReplay(cmd []string, wd string, quiet bool, debugInfoDirs []string
 // safeRemoveAll removes dir and its contents but only as long as dir does
 // not contain directories.
 func safeRemoveAll(dir string) {
-	dh, err := os.Open(dir)
+	fis, err := os.ReadDir(dir)
-	if err != nil {
-		return
-	}
-	defer dh.Close()
-	fis, err := dh.Readdir(-1)
 	if err != nil {
 		return
 	}

pkg/proc/test/support.go

@@ -279,12 +279,7 @@ func MustHaveRecordingAllowed(t testing.TB) {
 // SafeRemoveAll removes dir and its contents but only as long as dir does
 // not contain directories.
 func SafeRemoveAll(dir string) {
-	dh, err := os.Open(dir)
+	fis, err := os.ReadDir(dir)
-	if err != nil {
-		return
-	}
-	defer dh.Close()
-	fis, err := dh.Readdir(-1)
 	if err != nil {
 		return
 	}