Flip 32-bit warning string to let users know it’s the end of the line.

The string is changing to "This computer will no longer receive Google
Chrome updates because its hardware is no longer supported." Previously,
the message began with "This computer will soon stop receiving".

The new string has existed in Chrome for a long time in preparation for
this change, and it has already been translated.

BUG=425259

Review URL: https://codereview.chromium.org/663223002

Cr-Commit-Position: refs/heads/master@{#300357}

chrome/browser/mac/obsolete_system.h

@@ -45,9 +45,7 @@ class ObsoleteSystemMac {
 
   // true if this is the final release that will run on 32-bit-only systems.
   static bool Is32BitEndOfTheLine() {
-    // TODO(mark): Change to true immediately prior to the final build that
-    // supports 32-bit-only systems.
-    return false;
+    return true;
   }
 
  private: