remove obsolete workaround

The workaround is not needed anymore - mariadb requires bison 2.x.

And removing all __attribute__ in sql_yacc.yy breaks
new DBUG_ENTER.

sql/sql_yacc.yy

@@ -100,29 +100,6 @@ int yylex(void *yylval, void *yythd);
     MYSQL_YYABORT;                               \
   }
 
-/*
-  Work around for broken code generated by bison 1.875.
-
-  The code generated by bison 1.875a and later, bison 2.1 and bison 2.2 is ok.
-  With bison 1.875 however, the generated code contains:
-<pre>
-  yyerrlab1:
-  #if defined (__GNUC_MINOR__) && 2093 <= (__GNUC__ * 1000 + __GNUC_MINOR__)
-    __attribute__ ((__unused__))
-  #endif
-</pre>
-  This usage of __attribute__ is illegal, so we remove it.
-  See the following references for details:
-  http://lists.gnu.org/archive/html/bug-bison/2004-02/msg00014.html
-  http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14273
-*/
-
-#if defined (__GNUC_MINOR__) && 2093 <= (__GNUC__ * 1000 + __GNUC_MINOR__)
-#undef __attribute__
-#define __attribute__(X)
-#endif
-
-
 #ifndef DBUG_OFF
 #define YYDEBUG 1
 #else