Moved LB token changes solely into grpclb.c

src/core/ext/client_config/client_channel.c

src/core/ext/client_config/lb_policy.c

src/core/ext/client_config/lb_policy.h

src/core/ext/client_config/lb_policy_factory.h

src/core/ext/lb_policy/grpclb/grpclb.c

src/core/ext/lb_policy/pick_first/pick_first.c

src/core/ext/lb_policy/round_robin/round_robin.c

src/core/ext/resolver/dns/native/dns_resolver.c

src/core/ext/resolver/sockaddr/sockaddr_resolver.c

src/core/lib/transport/metadata.c

src/core/lib/transport/metadata.h