MM-10417 Improve HTTPService for use in image proxy (#9966)

* Replaced httpservice with proper http.Client

* Added HTTPService.MakeTransport

* Expose timeouts used by HTTPServiceImpl

* Add additional documentation to HTTPService

* Remove MockedHTTPService

* Fix missing license

app/helper_test.go

@@ -6,7 +6,6 @@ package app
 import (
 	"io"
 	"io/ioutil"
-	"net/http"
 	"os"
 	"path/filepath"
 	"time"
@@ -16,7 +15,6 @@ import (
 	"github.com/mattermost/mattermost-server/mlog"
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/utils"
-	"github.com/mattermost/mattermost-server/utils/testutils"
 )
 
 type TestHelper struct {
@@ -32,8 +30,6 @@ type TestHelper struct {
 
 	tempConfigPath string
 	tempWorkspace  string
-
-	MockedHTTPService *testutils.MockedHTTPService
 }
 
 func setupTestHelper(enterprise bool) *TestHelper {
@@ -133,13 +129,6 @@ func (me *TestHelper) InitBasic() *TestHelper {
 	return me
 }
 
-func (me *TestHelper) MockHTTPService(handler http.Handler) *TestHelper {
-	me.MockedHTTPService = testutils.MakeMockedHTTPService(handler)
-	me.App.HTTPService = me.MockedHTTPService
-
-	return me
-}
-
 func (me *TestHelper) MakeEmail() string {
 	return "success_" + model.NewId() + "@simulator.amazonses.com"
 }