Remove issue locking/unlocking preview media type.

These changes are now official, so the custom media type is no longer
needed.

Fixes #381.
Fixes #382.
Updates #279.

Change-Id: I33cad47c6645c5292f699826ae117b94260a3044

github/github.go

@@ -55,9 +55,6 @@ const (
 	// https://developer.github.com/changes/2015-11-11-protected-branches-api/
 	mediaTypeProtectedBranchesPreview = "application/vnd.github.loki-preview+json"
 
-	// https://developer.github.com/changes/2016-02-11-issue-locking-api/
-	mediaTypeIssueLockingPreview = "application/vnd.github.the-key-preview+json"
-
 	// https://help.github.com/enterprise/2.4/admin/guides/migrations/exporting-the-github-com-organization-s-repositories/
 	mediaTypeMigrationsPreview = "application/vnd.github.wyandotte-preview+json"
 

github/issues.go

@@ -289,9 +289,6 @@ func (s *IssuesService) Lock(owner string, repo string, number int) (*Response,
 		return nil, err
 	}
 
-	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeIssueLockingPreview)
-
 	return s.client.Do(req, nil)
 }
 
@@ -305,8 +302,5 @@ func (s *IssuesService) Unlock(owner string, repo string, number int) (*Response
 		return nil, err
 	}
 
-	// TODO: remove custom Accept header when this API fully launches.
-	req.Header.Set("Accept", mediaTypeIssueLockingPreview)
-
 	return s.client.Do(req, nil)
 }

github/issues_test.go

@@ -253,7 +253,6 @@ func TestIssuesService_Lock(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/issues/1/lock", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "PUT")
-		testHeader(t, r, "Accept", mediaTypeIssueLockingPreview)
 
 		w.WriteHeader(http.StatusNoContent)
 	})
@@ -269,7 +268,6 @@ func TestIssuesService_Unlock(t *testing.T) {
 
 	mux.HandleFunc("/repos/o/r/issues/1/lock", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "DELETE")
-		testHeader(t, r, "Accept", mediaTypeIssueLockingPreview)
 
 		w.WriteHeader(http.StatusNoContent)
 	})