Move OpenSSL locking code out of SSLContext

Summary:
OpenSSL 1.1.0 deprecates the callback based locking setup in favor
for platform native mutexes.

Added `OPENSSL_init_ssl` in the OpenSSL portability module for OpenSSL API < 1.1.0. This implements
the standard OpenSSL library initialization routines (taken from SSLContext::initializeOpenSSL).

Added `OPENSSL_cleanup` in the OpenSSL portability module for OpenSSL API < 1.1.0. This implements
the cleanup routine from SSLContext::cleanupOpenSSL.

Removed `SSLContext::SSLLockType`. Replaced with `folly::ssl::LockType`.

Reviewed By: mzlee, ngoyal

Differential Revision: D5404777

fbshipit-source-id: 7e5d9bf4a6683afb5560ada0a5b73cac3ff2662b