symbol.h: remove stale symbol deleted at r47913

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63104 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

symbol.h

@@ -98,8 +98,6 @@ is_global_name_punct(const int c)
     return (ruby_global_name_punct_bits[(c - 0x20) / 32] >> (c % 32)) & 1;
 }
 
-ID rb_intern_cstr_without_pindown(const char *, long, rb_encoding *);
-
 RUBY_SYMBOL_EXPORT_BEGIN
 
 size_t rb_sym_immortal_count(void);