Get rid of strDocu.

libraries/config.default.php

@@ -2329,7 +2329,7 @@ $cfg['ErrorIconic'] = true;
 $cfg['MainPageIconic'] = true;
 
 /**
- * show help button instead of strDocu (true|false)?
+ * show help button instead of Documentation text (true|false)?
  *
  * @global boolean $cfg['ReplaceHelpImg']
  */

libraries/messages.inc.php

@@ -18,8 +18,6 @@ $charset = 'utf-8';
 /* l10n: Text direction, use either ltr or rtl */
 $text_dir = __('ltr');
 
-$strDocu = __('Documentation');
-
 $strLatexContent = __('Content of table __TABLE__');
 $strLatexContinued = __('(continued)');
 $strLatexStructure = __('Structure of table __TABLE__');