Remove custom Accept header for hide comment preview API

This is not part of the main API. This is to help test runatlantis#1009 For some reason API calls come back with '406 Not Acceptable Body' on Github Enterprise, despite the GE stating the custom Accept headers are required.

Maybe it's no longer required like on github.com and GH simply forgot to update the docs?

server/events/vcs/github_client.go

@@ -22,10 +22,10 @@ import (
 	"github.com/runatlantis/atlantis/server/events/models"
 	"github.com/runatlantis/atlantis/server/events/vcs/common"
 
-	"github.com/Laisky/graphql"
 	"github.com/google/go-github/v28/github"
 	"github.com/pkg/errors"
 	"github.com/shurcooL/githubv4"
+	"github.com/shurcooL/graphql"
 )
 
 // maxCommentLength is the maximum number of chars allowed in a single comment
@@ -66,18 +66,7 @@ func NewGithubClient(hostname string, user string, pass string) (*GithubClient,
 		}
 	}
 
-	// shurcooL's githubv4 library has a client ctor, but it doesn't support schema
-	// previews, which need custom Accept headers (https://developer.github.com/v4/previews)
-	// So for now use the graphql client, since the githubv4 library was basically
-	// a simple wrapper around it. And instead of using shurcooL's graphql lib, use
-	// Laisky's, since shurcooL's doesn't support custom headers.
-	// Once the Minimize Comment schema is official, this can revert back to using
-	// shurcooL's libraries completely.
-	v4MutateClient := graphql.NewClient(
-		graphqlURL,
-		tp.Client(),
-		graphql.WithHeader("Accept", "application/vnd.github.queen-beryl-preview+json"),
-	)
+	v4MutateClient := graphql.NewClient(graphqlURL, tp.Client())
 
 	return &GithubClient{
 		user:           user,

server/events/vcs/github_client_test.go

@@ -261,11 +261,6 @@ func TestGithubClient_HideOldComments(t *testing.T) {
 				w.Write([]byte(issueResp)) // nolint: errcheck
 				return
 			case "POST /graphql":
-				if accept, has := r.Header["Accept"]; !has || accept[0] != "application/vnd.github.queen-beryl-preview+json" {
-					t.Error("missing preview header")
-					http.Error(w, "bad request", http.StatusBadRequest)
-					return
-				}
 				defer r.Body.Close() // nolint: errcheck
 				body, err := ioutil.ReadAll(r.Body)
 				if err != nil {