Remove a couple of unused/barely used names.

sql/sql_lex.cc:
  Remove an unused thread key.
sql/sql_lex.h:
  Remove an unused thread key, current_lex.
sql/sql_parse.cc:
  Remove an unused thread key, current_lex macro.

sql/sql_lex.cc

@@ -41,8 +41,6 @@ sys_var_long_ptr trg_new_row_fake_var(0, 0);
 #define yySkip()	lex->ptr++
 #define yyLength()	((uint) (lex->ptr - lex->tok_start)-1)
 
-pthread_key(LEX*,THR_LEX);
-
 /* Longest standard keyword name */
 #define TOCK_NAME_LENGTH 24
 
@@ -91,8 +89,6 @@ void lex_init(void)
   for (i=0 ; i < array_elements(sql_functions) ; i++)
     sql_functions[i].length=(uchar) strlen(sql_functions[i].name);
 
-  VOID(pthread_key_create(&THR_LEX,NULL));
-
   DBUG_VOID_RETURN;
 }
 

sql/sql_lex.h

@@ -1116,6 +1116,3 @@ extern void lex_start(THD *thd, uchar *buf,uint length);
 extern void lex_end(LEX *lex);
 extern int MYSQLlex(void *arg, void *yythd);
 
-extern pthread_key(LEX*,THR_LEX);
-
-#define current_lex (current_thd->lex)

sql/sql_parse.cc

@@ -2365,7 +2365,7 @@ static void reset_one_shot_variables(THD *thd)
 
 
 /*
-  Execute command saved in thd and current_lex->sql_command
+  Execute command saved in thd and lex->sql_command
 
   SYNOPSIS
     mysql_execute_command()
@@ -5541,7 +5541,7 @@ bool check_stack_overrun(THD *thd, long margin,
 
 bool my_yyoverflow(short **yyss, YYSTYPE **yyvs, ulong *yystacksize)
 {
-  LEX	*lex=current_lex;
+  LEX	*lex= current_thd->lex;
   ulong old_info=0;
   if ((uint) *yystacksize >= MY_YACC_MAX)
     return 1;
@@ -5978,7 +5978,7 @@ bool add_field_to_list(THD *thd, char *field_name, enum_field_types type,
 
 void store_position_for_column(const char *name)
 {
-  current_lex->last_field->after=my_const_cast(char*) (name);
+  current_thd->lex->last_field->after=my_const_cast(char*) (name);
 }
 
 bool