Doc fixes for process functions (Bug#30349)

Doc fixes for process functions (Bug#30349)

* doc/lispref/processes.texi (Asynchronous Processes): Explain what
the 'stopped' state means for a pipe process.
* src/process.c (Fmake_process, Fmake_pipe_process)
(Fmake_serial_process, Fmake_network_process):
* lisp/subr.el (start-process):
* lisp/net/tls.el (open-tls-stream):
* lisp/net/starttls.el (starttls-open-stream):
* lisp/net/gnutls.el (open-gnutls-stream): Remove meaningless phrase
"specify an output stream" phrase from docstring.