This change removes the old ASN.1 functions (ASN1_seq_unpack and
ASN1_seq_pack) which have always been disabled in BoringSSL.

It also removes code enabled by OPENSSL_EXPORT_VAR_AS_FUNCTION, which
we have never used.

Change-Id: I1fe323abf945a8a5828a04cc195c072e100a5095
Reviewed-on: https://boringssl-review.googlesource.com/1556
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)