Don't call CRYPTO_add in BoringSSL.

The old OpenSSL threading hooks were removed in favor of the library knowing
about threads internally. Instead of CRYPTO_add, use FOO_up_ref wrappers that
don't require reaching into the type.

BUG=none
R=jiayl@webrtc.org, juberti@google.com

Review URL: https://webrtc-codereview.appspot.com/54579004

Cr-Commit-Position: refs/heads/master@{#9324}