Remove redundant special handling of OP_ARGELEM from tokenizer

Previously, the op fragments created here were woven into the signature handling part of the final optree and had to contain a few extra fields related to signature argument handling. Since `subsignature_finish()` now creates the entire optree itself, the ops created by the tokenizer are only used for their side-effect of containing the pad offset in `op_targ`. As such, they no longer need to be specially sized OP_ARGELEM and can be regular OP_PADANYs.

Author: leonerd

toke.c

@@ -9997,25 +9997,7 @@ S_pending_ident(pTHX)
  GCC_DIAG_RESTORE_STMT;
  }
 
- if (PL_in_my == KEY_sigvar) {
- /* A signature 'padop' needs in addition, an op_first to
- * point to a child sigdefelem, and an extra field to hold
- * the signature index. We can achieve both by using an
- * UNOP_AUX and (ab)using the op_aux field to hold the
- * index. If we ever need more fields, use a real malloced
- * aux strut instead.
- */
- assert(PL_parser->signature);
- /* We don't yet know the argindex but subsignature_append_*()
- * will fill it in
- */
- o = newUNOP_AUX(OP_ARGELEM, 0, NULL, NULL);
- o->op_private |= ( PL_tokenbuf[0] == '$' ? OPpARGELEM_SV
- : PL_tokenbuf[0] == '@' ? OPpARGELEM_AV
- : OPpARGELEM_HV);
- }
- else
- o = newOP(OP_PADANY, 0);
+ o = newOP(OP_PADANY, 0);
  o->op_targ = allocmy(PL_tokenbuf, tokenbuf_len,
  UTF ? SVf_UTF8 : 0);
  if (PL_in_my == KEY_sigvar)