py/lexer: Permanently disable the mp_lexer_show_token function.

The lexer is very mature and this debug function is no longer used.  If
it's really needed one can uncomment it and recompile.

py/lexer.c

@@ -792,7 +792,9 @@ void mp_lexer_to_next(mp_lexer_t *lex) {
     mp_lexer_next_token_into(lex, false);
 }
 
-#if MICROPY_DEBUG_PRINTERS
+#if 0
+// This function is used to print the current token and should only be
+// needed to debug the lexer, so it's not available via a config option.
 void mp_lexer_show_token(const mp_lexer_t *lex) {
     printf("(" UINT_FMT ":" UINT_FMT ") kind:%u str:%p len:%zu", lex->tok_line, lex->tok_column, lex->tok_kind, lex->vstr.buf, lex->vstr.len);
     if (lex->vstr.len > 0) {

py/lexer.h

@@ -172,7 +172,6 @@ mp_lexer_t *mp_lexer_new_from_str_len(qstr src_name, const char *str, mp_uint_t
 
 void mp_lexer_free(mp_lexer_t *lex);
 void mp_lexer_to_next(mp_lexer_t *lex);
-void mp_lexer_show_token(const mp_lexer_t *lex);
 
 /******************************************************************/
 // platform specific import function; must be implemented for a specific port

py/mpconfig.h

@@ -362,7 +362,6 @@
 #endif
 
 // Whether to build functions that print debugging info:
-//   mp_lexer_show_token
 //   mp_bytecode_print
 //   mp_parse_node_print
 #ifndef MICROPY_DEBUG_PRINTERS