Command docs: fix up command references

Command docs: fix up command references

Almost all OpenSSL commands are in reality 'openssl cmd', so make sure
they are refered to like that and not just as the sub-command.

Self-references are avoided as much as is possible, and replaced with
"this command".  In some cases, we even avoid that with a slight
rewrite of the sentence or paragrah they were in.  However, in the few
cases where a self-reference is still admissible, they are done in
bold, i.e. openssl-speed.pod references itself like this:

    B<openssl speed>

References to other commands are done as manual links, i.e. CA.pl.pod
references 'openssl req' like this: L<openssl-req(1)>

Some commands are examples rather than references; we enclose those in
C<>.

While we are it, we abolish "utility", replacing it with "command", or
remove it entirely in some cases.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/10065)