Make CBS_get_any_asn1_element accept only DER.

This change makes |CBS_get_any_asn1_element| only handle DER elements.
Another function, |CBS_get_any_ber_asn1_element| is exposed internally
for the cases where we need to process BER data.

Change-Id: I544141a1a3d7913986352a8fd9a6d00b9f282652
Reviewed-on: https://boringssl-review.googlesource.com/4994
Reviewed-by: Adam Langley <agl@google.com>
4 files changed