Revert "Bug 26962: Circuit display onboarding (part 2)."

Remove strings that were used for the "New Circuit Display" promotional
banner which previously was shown on the about:tbupdate page.

This reverts commit c93f0641.

src/chrome/locale/en-US/aboutTBUpdate.dtd

@@ -4,7 +4,3 @@
 <!ENTITY aboutTBUpdate.linkLabel  "visit our website">
 <!ENTITY aboutTBUpdate.linkSuffix ".">
 <!ENTITY aboutTBUpdate.changeLogHeading "Changelog:">
-
-<!ENTITY aboutTBUpdate.circuitDisplayHeading "New, Redesigned Circuit Display">
-<!ENTITY aboutTBUpdate.circuitDisplayDescription "The Tor circuit display has been relocated and improved! Click the Site&#160;Identity button (located on the left side of the URL bar) to see the new circuit display.">
-<!ENTITY aboutTBUpdate.learnMore "Learn More">