Make efFormatNumParserFunction_Setup static

Running phpunit gives Strict standards: call_user_func_array()
expects parameter 1 to be a valid callback, non-static method
FormatNumHooks::efFormatNumParserFunction_Setup() should not
be called statically in mediawiki/includes/Hooks.php on line 207

Change-Id: I81cc113376689b775f6d00948e4a9244b105dadc