Remove unused functions from `struct rb_parser_config_struct`

ruby_parser.c

@@ -184,12 +184,6 @@ intern3(const char *name, long len, void *enc)
     return rb_intern3(name, len, (rb_encoding *)enc);
 }
 
-static int
-encoding_is_ascii8bit(VALUE obj)
-{
-    return ENCODING_IS_ASCII8BIT(obj);
-}
-
 static void *
 usascii_encoding(void)
 {
@@ -430,7 +424,6 @@ static const rb_parser_config_t rb_global_parser_config = {
     .enc_isspace = enc_isspace,
     .enc_coderange_7bit = ENC_CODERANGE_7BIT,
     .enc_coderange_unknown = ENC_CODERANGE_UNKNOWN,
-    .encoding_is_ascii8bit = encoding_is_ascii8bit,
     .usascii_encoding = usascii_encoding,
     .enc_coderange_broken = ENC_CODERANGE_BROKEN,
     .enc_mbminlen = enc_mbminlen,

rubyparser.h

@@ -1340,7 +1340,6 @@ typedef struct rb_parser_config_struct {
     int (*enc_find_index)(const char *name);
     rb_encoding *(*enc_from_index)(int idx);
     int (*enc_isspace)(OnigCodePoint c, rb_encoding *enc);
-    int (*encoding_is_ascii8bit)(VALUE obj);
     rb_encoding *(*usascii_encoding)(void);
     int enc_coderange_broken;
     int (*enc_mbminlen)(rb_encoding *enc);

universal_parser.c

@@ -173,7 +173,6 @@
 #define rb_enc_isspace          p->config->enc_isspace
 #define ENC_CODERANGE_7BIT      p->config->enc_coderange_7bit
 #define ENC_CODERANGE_UNKNOWN   p->config->enc_coderange_unknown
-#define ENCODING_IS_ASCII8BIT   p->config->encoding_is_ascii8bit
 #define rb_usascii_encoding     p->config->usascii_encoding
 
 #define rb_local_defined          p->config->local_defined