MM-11272 Add OpenGraph and image dimension metadata to posts (#9313)

* Move OpenGraph code into its own file

* Move OpenGraph image proxying to app layer

* Move test file code out of api4 package

* MM-11272 Add OpenGraph and image dimension metadata to posts

api4/apitestlib.go

@@ -4,7 +4,6 @@
 package api4
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -746,22 +745,6 @@ func CheckInternalErrorStatus(t *testing.T, resp *model.Response) {
 	}
 }
 
-func readTestFile(name string) ([]byte, error) {
-	path, _ := utils.FindDir("tests")
-	file, err := os.Open(filepath.Join(path, name))
-	if err != nil {
-		return nil, err
-	}
-	defer file.Close()
-
-	data := &bytes.Buffer{}
-	if _, err := io.Copy(data, file); err != nil {
-		return nil, err
-	} else {
-		return data.Bytes(), nil
-	}
-}
-
 // Similar to s3.New() but allows initialization of signature v2 or signature v4 client.
 // If signV2 input is false, function always returns signature v4.
 //