drop versions older than 1.62 (#2405)

hscontrol/capver/capver.go

@@ -9,6 +9,20 @@ import (
 	"tailscale.com/util/set"
 )
 
+const MinSupportedCapabilityVersion tailcfg.CapabilityVersion = 88
+
+// CanOldCodeBeCleanedUp is intended to be called on startup to see if
+// there are old code that can ble cleaned up, entries should contain
+// a CapVer where something can be cleaned up and a panic if it can.
+// This is only intended to catch things in tests.
+//
+// All uses of Capability version checks should be listed here.
+func CanOldCodeBeCleanedUp() {
+	if MinSupportedCapabilityVersion >= 111 {
+		panic("LegacyDERP can be cleaned up in tail.go")
+	}
+}
+
 func tailscaleVersSorted() []string {
 	vers := xmaps.Keys(tailscaleToCapVer)
 	sort.Strings(vers)

hscontrol/capver/capver_test.go

@@ -15,6 +15,19 @@ func TestTailscaleLatestMajorMinor(t *testing.T) {
 	}{
 		{3, false, []string{"v1.76", "v1.78", "v1.80"}},
 		{2, true, []string{"1.78", "1.80"}},
+		// Lazy way to see all supported versions
+		{10, true, []string{
+			"1.62",
+			"1.64",
+			"1.66",
+			"1.68",
+			"1.70",
+			"1.72",
+			"1.74",
+			"1.76",
+			"1.78",
+			"1.80",
+		}},
 		{0, false, nil},
 	}