feature/featuretags, all: add ts_omit_acme to disable TLS cert support

I'd started to do this in the earlier ts_omit_server PR but
decided to split it into this separate PR.

Updates #17128

Change-Id: Ief8823a78d1f7bbb79e64a5cab30a7d0a5d6ff4b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/deps_test.go

@@ -108,3 +108,16 @@ func TestOmitPortmapper(t *testing.T) {
 		},
 	}.Check(t)
 }
+
+func TestOmitACME(t *testing.T) {
+	deptest.DepChecker{
+		GOOS:   "linux",
+		GOARCH: "amd64",
+		Tags:   "ts_omit_acme,ts_include_cli",
+		OnDep: func(dep string) {
+			if strings.Contains(dep, "/acme") {
+				t.Errorf("unexpected dep with ts_omit_acme: %q", dep)
+			}
+		},
+	}.Check(t)
+}