(Re)move some things from e_os.h

Remove GETPID_IS_MEANINGLESS and osslargused.

Move socket-related things to new file internal/sockets.h; this is now
only needed by four(!!!) files.  Compiles should be a bit faster.
Remove USE_SOCKETS ifdef's

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4209)