The dtls1_output_cert_chain function no longer exists so remove it from ssl_locl.h

(Imported from upstream's 789da2c73d875af59b14156b6295aa4bdfc4f424)

Change-Id: Id94877d8d22578e23c63d1f133820a89ceae29ae
Reviewed-on: https://boringssl-review.googlesource.com/2834
Reviewed-by: Adam Langley <agl@google.com>