all: update to Go 1.20, use strings.CutPrefix/Suffix instead of our fork

Updates #7123
Updates #5309

Change-Id: I90bcd87a2fb85a91834a0dd4be6e03db08438672
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

util/deephash/deephash_test.go

@@ -1001,11 +1001,11 @@ func FuzzTime(f *testing.F) {
 	) {
 		t1 := time.Unix(s1, ns1)
 		if loc1 {
-			t1.In(time.FixedZone(name1, off1))
+			_ = t1.In(time.FixedZone(name1, off1))
 		}
 		t2 := time.Unix(s2, ns2)
 		if loc2 {
-			t2.In(time.FixedZone(name2, off2))
+			_ = t2.In(time.FixedZone(name2, off2))
 		}
 		got := Hash(&t1) == Hash(&t2)
 		want := t1.Format(time.RFC3339Nano) == t2.Format(time.RFC3339Nano)

util/strs/strs.go

@@ -1,35 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-// Package strs contains string-related utility funcs.
-package strs
-
-import "strings"
-
-// CutPrefix returns s without the provided leading prefix string
-// and reports whether it found the prefix.
-// If s doesn't start with prefix, CutPrefix returns s, false.
-// If prefix is the empty string, CutPrefix returns s, true.
-//
-// TODO: remove this once Go 1.20 is out with it.
-// See https://github.com/tailscale/tailscale/issues/5309
-func CutPrefix(s, prefix string) (after string, found bool) {
-	if !strings.HasPrefix(s, prefix) {
-		return s, false
-	}
-	return s[len(prefix):], true
-}
-
-// CutSuffix returns s without the provided ending suffix string
-// and reports whether it found the suffix.
-// If s doesn't end with suffix, CutSuffix returns s, false.
-// If suffix is the empty string, CutSuffix returns s, true.
-//
-// See https://github.com/tailscale/tailscale/issues/5309
-// TODO: remove this once Go 1.20 is out with it.
-func CutSuffix(s, suffix string) (before string, found bool) {
-	if !strings.HasSuffix(s, suffix) {
-		return s, false
-	}
-	return s[:len(s)-len(suffix)], true
-}

util/strs/strs_test.go

@@ -1,29 +0,0 @@
-// Copyright (c) Tailscale Inc & AUTHORS
-// SPDX-License-Identifier: BSD-3-Clause
-
-package strs
-
-import "testing"
-
-func TestCut(t *testing.T) {
-	tests := []struct {
-		fn       func(string, string) (string, bool)
-		in1, in2 string
-		want     string
-		wantOK   bool
-	}{
-		{CutPrefix, "foo", "fo", "o", true},
-		{CutPrefix, "bar", "fo", "bar", false},
-		{CutSuffix, "foo", "o", "fo", true},
-		{CutSuffix, "bar", "fo", "bar", false},
-	}
-	for i, tt := range tests {
-		got, gotOK := tt.fn(tt.in1, tt.in2)
-		if got != tt.want {
-			t.Errorf("%d. got %q; want %q", i, got, tt.want)
-		}
-		if gotOK != tt.wantOK {
-			t.Errorf("%d. got %v; want %v", i, gotOK, tt.wantOK)
-		}
-	}
-}