DevTools: remove WI.SourcesView._currentUISourceCode

Since WI.SourcesView._currentUISourceCode duplicates the currentFile
value inside WI.TabbedEditorContainer, there's no need for it.

BUG=none
R=pfeldman, dgozman

Review-Url: https://codereview.chromium.org/2157283002
Cr-Commit-Position: refs/heads/master@{#406328}
2 files changed