(create_process): Don't setup raw-text coding here.

(create_process): Don't setup raw-text coding here.
(Fopen_network_stream): Don't set coding->src_multibyte and
coding->dst_multibyte here.
(read_process_output): For process filter, return unibyte string
if default-enable-multibyte-characters is nil.
(send_process): If OBJECT is multibyte text, be sure to encoded it
by the specified coding system for the process.  Otherwise, setup
raw-text coding.
(init_process): Don't initialize default-process-coding-system
here.