Remove d_initial from the parser as it is unused (GH-12212)

d_initial, the first state of a particular DFA in the parser has always been initialized to 0 in the old pgen as well as the new pgen. As this value is not used and the first state of each DFA is assumed to be the first element in the array representing it, remove d_initial from the parser to reduce complexity.

Include/grammar.h

@@ -50,7 +50,6 @@ typedef struct {
 typedef struct {
     int          d_type;        /* Non-terminal this represents */
     char        *d_name;        /* For printing */
-    int          d_initial;     /* Initial state */
     int          d_nstates;
     state       *d_state;       /* Array of states */
     bitset       d_first;

Modules/parsermodule.c

@@ -662,7 +662,7 @@ validate_node(node *tree)
     REQ(tree, nt_dfa->d_type);
 
     /* Run the DFA for this nonterminal. */
-    dfa_state = &nt_dfa->d_state[nt_dfa->d_initial];
+    dfa_state = nt_dfa->d_state;
     for (pos = 0; pos < nch; ++pos) {
         node *ch = CHILD(tree, pos);
         int ch_type = TYPE(ch);

Parser/pgen/grammar.py

@@ -97,7 +97,7 @@ class Grammar:
                 '    {{{dfa_symbol}, "{symbol_name}", '.format(
                     dfa_symbol=symbol, symbol_name=self.number2symbol[symbol]
                 )
-                + "0, {n_states}, states_{dfa_index},\n".format(
+                + "{n_states}, states_{dfa_index},\n".format(
                     n_states=len(dfa), dfa_index=dfaindex
                 )
                 + '     "'