Merge pull request #10627 from jboeuf/more_ssl_factory_cleanup

include/grpc/grpc_security.h

src/core/lib/http/httpcli_security_connector.c

src/core/lib/security/credentials/ssl/ssl_credentials.c

src/core/lib/security/transport/security_connector.c

src/core/lib/security/transport/security_connector.h

src/core/tsi/ssl_transport_security.c

src/core/tsi/ssl_transport_security.h