Prevent IE from going back on backspace

This closes https://github.com/select2/select2/issues/3168.

dist/js/select2.full.js

@@ -1786,6 +1786,8 @@ S2.define('select2/selection/search',[
           var item = $previousChoice.data('data');
 
           self.searchRemoveChoice(item);
+
+          evt.preventDefault();
         }
       }
     });

dist/js/select2.js

@@ -1786,6 +1786,8 @@ S2.define('select2/selection/search',[
           var item = $previousChoice.data('data');
 
           self.searchRemoveChoice(item);
+
+          evt.preventDefault();
         }
       }
     });

src/js/select2/selection/search.js

@@ -75,6 +75,8 @@ define([
           var item = $previousChoice.data('data');
 
           self.searchRemoveChoice(item);
+
+          evt.preventDefault();
         }
       }
     });