Scanner and parser use different tables for constants

Moreover, each function being parsed has its own table.

The code is cleaner when each table is used for one specific purpose:
The scanner uses its table to anchor and unify strings, mapping strings
to themselves; the parser uses it to reuse constants in the code,
mapping constants to their indices in the constant table. A different
table for each task avoids false collisions.

ltable.h

@@ -154,8 +154,6 @@ LUAI_FUNC lu_byte luaH_getint (Table *t, lua_Integer key, TValue *res);
 /* Special get for metamethods */
 LUAI_FUNC const TValue *luaH_Hgetshortstr (Table *t, TString *key);
 
-LUAI_FUNC TString *luaH_getstrkey (Table *t, TString *key);
-
 LUAI_FUNC int luaH_psetint (Table *t, lua_Integer key, TValue *val);
 LUAI_FUNC int luaH_psetshortstr (Table *t, TString *key, TValue *val);
 LUAI_FUNC int luaH_psetstr (Table *t, TString *key, TValue *val);