Eliminate redundant places where server name was stored.

include/grpc/impl/codegen/grpc_types.h

src/core/ext/client_channel/http_connect_handshaker.c

src/core/ext/client_channel/http_connect_handshaker.h

src/core/ext/client_channel/resolver_registry.c

src/core/ext/client_channel/resolver_registry.h

src/core/ext/client_channel/subchannel.h

src/core/ext/client_channel/subchannel_index.c

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/ext/transport/chttp2/client/chttp2_connector.c

src/core/ext/transport/chttp2/client/chttp2_connector.h

...ore/ext/transport/chttp2/client/insecure/channel_create.c

...xt/transport/chttp2/client/secure/secure_channel_create.c

test/core/end2end/fake_resolver.c