drop long-deprecated gpgsm-gencert.sh

* tools/gpgsm-gencert.sh: remove deprecated script entirely.  It is
   fully replaced by gpgsm --gen-key
 * doc/tools.texi: remove gpgsm-gencert.sh documentation
 * .gitignore: no longer ignore gpgsm-gencert.sh manpage
 * doc/Makefile.am: quit making the manpage
 * tools/Makefile.am: quit distributing the script
 * doc/howto-create-a-server-cert.texi: overhaul documentation to use
   gpgsm --gen-key and tweak explanations

--

The commit deprecating gpgsm-gencert.sh
(81972ca7d5) dates back exactly 6 years.

 https://codesearch.debian.net/results/gpgsm-gencert.sh

suggests that in all of debian it is only referenced in documentation
(for poldi and scute) and example files (libept), and isn't actually
used directly anywhere.

Furthermore, trying to use gpgsm-gencert.sh to make a simple webserver
certificate-signing request failed for me, following the examples in
doc/howto-create-a-server-cert.texi exactly.

It's time we ripped off this band-aid :)

Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>

doc/tools.texi

@@ -15,7 +15,6 @@ GnuPG comes with a couple of smaller tools:
 * addgnupghome::          Create .gnupg home directories.
 * gpgconf::               Modify .gnupg home directories.
 * applygnupgdefaults::    Run gpgconf for all users.
-* gpgsm-gencert.sh::      Generate an X.509 certificate request.
 * gpg-preset-passphrase:: Put a passphrase into the cache.
 * gpg-connect-agent::     Communicate with a running agent.
 * dirmngr-client::        How to use the Dirmngr client tool.
@@ -1000,42 +999,6 @@ applygnupgdefaults
 @end example
 
 
-@c
-@c    GPGSM-GENCERT.SH
-@c
-@node gpgsm-gencert.sh
-@section Generate an X.509 certificate request
-@manpage gpgsm-gencert.sh.1
-@ifset manverb
-.B gpgsm-gencert.sh
-\- Generate an X.509 certificate request
-@end ifset
-
-@mansect synopsis
-@ifset manverb
-.B  gpgsm-gencert.sh
-@end ifset
-
-@mansect description
-This is a simple tool to interactively generate a certificate request
-which will be printed to stdout.
-
-@manpause
-@noindent
-@command{gpgsm-gencert.sh} is invoked as:
-
-@samp{gpgsm-cencert.sh}
-
-@mansect see also
-@ifset isman
-@command{gpgsm}(1),
-@command{gpg-agent}(1),
-@command{scdaemon}(1)
-@end ifset
-@include see-also-note.texi
-
-
-
 @c
 @c   GPG-PRESET-PASSPHRASE
 @c