Bug 875469 Remove bogus attribute r=Mossop

DONTBUILD because preffed off by default

toolkit/components/filepicker/content/filepicker.xul

@@ -73,7 +73,7 @@
 </grid>
 <hbox class="dialog-button-box" align="center">
   <checkbox label="&showHiddenFiles.label;" oncommand="toggleShowHidden();"
-            flex="1" align="left"  accesskey="&showHiddenFiles.accesskey;"/>
+            flex="1" accesskey="&showHiddenFiles.accesskey;"/>
   <button dlgtype="cancel" icon="cancel" class="dialog-button"/>
   <button dlgtype="accept" icon="open" class="dialog-button"/>
 </hbox>