Remove declarations of undefined functions

- mrb_cmpint, mrb_cmperr: removed (b43e790b717ff373ff1c41cc8e16ead7e825f61e)
- mrb_parser_filename: has been replaced by mrbc_filename (65096c4c1bd1bfb6f547808fc01ab6ea223d9dc6)
- mrb_hash: removed (b7d5ccdb36528b2ab0009e4ec443b53e91ffb89e)
- mrb_obj_is_proc: undefined since first commit
- mrb_str_hash_cmp: removed (64fc4ac332eab0be7704cf6f7ec5a96c523c0ed9)