Merge bitcoin#765: remove dead store in ecdsa_signature_parse_der_lax

f00d657 remove dead store in ecdsa_signature_parse_der_lax (fanquake)

Pull request description:

ACKs for top commit:
  elichai:
    utACK f00d657, it does look like we don't use that assignment
  jonasnick:
    ACK f00d657

Tree-SHA512: 9aa54c901f299341c309411b0247720f5152a131dd346c19be7ee21865e3a822e8cf91b869e28ef6288adaf31660bc2e18874e304052468a9be6b7027674af30

contrib/lax_der_parsing.c

@@ -112,7 +112,6 @@ int ecdsa_signature_parse_der_lax(const secp256k1_context* ctx, secp256k1_ecdsa_
         return 0;
     }
     spos = pos;
-    pos += slen;
 
     /* Ignore leading zeroes in R */
     while (rlen > 0 && input[rpos] == 0) {