Revert "Grand unified closures"

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.gemspec

include/grpc/impl/codegen/atm.h

include/grpc/impl/codegen/atm_gcc_atomic.h

include/grpc/impl/codegen/atm_gcc_sync.h

include/grpc/impl/codegen/atm_windows.h

package.xml

src/core/ext/client_config/client_channel.c

src/core/ext/client_config/subchannel.c

src/core/ext/transport/chttp2/transport/chttp2_transport.c

src/core/ext/transport/chttp2/transport/internal.h

src/core/ext/transport/chttp2/transport/parsing.c

src/core/ext/transport/chttp2/transport/stream_lists.c

src/core/ext/transport/chttp2/transport/writing.c