Remove unused pref (part of bug 250637).

r=mscott

mail/app/profile/all-thunderbird.js

@@ -252,7 +252,6 @@ pref("browser.search.defaulturl", "chrome://navigator-region/locale/region.prope
 pref("browser.search.opensidebarsearchpanel", true);
 pref("browser.search.last_search_category", "NC:SearchCategory?category=urn:search:category:1");
 pref("browser.search.mode", 0);
-pref("browser.search.powermode", 0);
 // basic search popup constraint: minimum sherlock plugin version displayed
 // (note: must be a string representation of a float or it'll default to 0.0)
 pref("browser.search.basic.min_ver", "0.0");