Bug 1160774 - Don't wait for 'stylesheet-selected' event in source-utils.js as it is not emitted if the requested sheet is already selected. r=jsantell

The promise returned by selectStyleSheet resolves about the same time as the
'stylesheet-selected' event would be emitted so there's no need to wait for the
actual event that might never come.

browser/devtools/shared/source-utils.js

@@ -25,10 +25,8 @@ exports.viewSourceInStyleEditor = Task.async(function *(toolbox, sourceURL, sour
   let panel = yield toolbox.loadTool("styleeditor");
 
   try {
-    let selected = panel.UI.once("editor-selected");
     yield panel.selectStyleSheet(sourceURL, sourceLine);
     yield toolbox.selectTool("styleeditor");
-    yield selected;
     return true;
   } catch (e) {
     exports.viewSource(toolbox, sourceURL, sourceLine);