netns_linux: remove special handling for tests.

With netns handling localhost now, existing tests no longer
need special handling. The tests set up their connections to
localhost, and the connections work without fuss.

Remove the special handling for tests.

Also remove the hostinfo.TestCase support, since this was
the only use of it. It can be added back later if really
needed, but it would be better to try to make tests work
without special cases.

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

hostinfo/hostinfo.go

@@ -9,7 +9,6 @@
 package hostinfo
 
 import (
-	"flag"
 	"io"
 	"os"
 	"runtime"
@@ -29,7 +28,6 @@ const (
 	Heroku          = EnvType("hr")
 	AzureAppService = EnvType("az")
 	AWSFargate      = EnvType("fg")
-	TestCase        = EnvType("tc")
 )
 
 var envType atomic.Value // of EnvType
@@ -44,11 +42,6 @@ func GetEnvType() EnvType {
 }
 
 func getEnvType() EnvType {
-	// inTestCase needs to go first. If running tests in a container, we want
-	// the environment to be TestCase not the type of container.
-	if inTestCase() {
-		return TestCase
-	}
 	if inKnative() {
 		return KNative
 	}
@@ -91,13 +84,6 @@ func InContainer() bool {
 	return ret
 }
 
-func inTestCase() bool {
-	if flag.CommandLine.Lookup("test.v") != nil {
-		return true
-	}
-	return false
-}
-
 func inKnative() bool {
 	// https://cloud.google.com/run/docs/reference/container-contract#env-vars
 	if os.Getenv("K_REVISION") != "" && os.Getenv("K_CONFIGURATION") != "" &&