Revert "tech: use context package over xperimental version"

This reverts commit 99f1c30071e770a30abfb86b00e5aaf2dd150253.

pkg/api/login_oauth.go

@@ -12,7 +12,7 @@ import (
 	"net/http"
 	"net/url"
 
-	"context"
+	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 
 	"github.com/grafana/grafana/pkg/bus"

pkg/social/social.go

@@ -4,7 +4,7 @@ import (
 	"net/http"
 	"strings"
 
-	"context"
+	"golang.org/x/net/context"
 	"golang.org/x/oauth2"
 
 	"github.com/grafana/grafana/pkg/setting"