system: Remove nss-certs from OS templates, adjust doc.

This is a follow-up to commit 86afaadb51 ("system: Add 'nss-certs' to
%base-packages-networking.")

* doc/guix-cookbook.texi (Running Guix on a Linode Server): Remove nss-certs
from operating system's packages field.
(Running Guix on a Kimsufi Server): Likewise.
* doc/guix.texi (Using the Configuration System): Likewise.
(X.509 Certificates): Adjust to mention nss-certs *is* part of %base-packages.
* gnu/installer/services.scm (%system-services): Remove recommendation to
install nss-certs.
* gnu/system/examples/bare-bones.tmpl (host-name): Remove obsolete comments.
* gnu/system/examples/desktop.tmpl (packages): Remove nss-certs.
* gnu/system/examples/lightweight-desktop.tmpl (packages): Likewise.
* gnu/system/examples/plasma.tmpl (packages): Likewise.
* gnu/system/examples/raspberry-pi-64-nfs-root.tmpl (packages): Likewise.
* gnu/system/examples/raspberry-pi-64.tmpl (packages): Likewise.
* gnu/system/examples/vm-image.tmpl (packages): Likewise.
* gnu/system/images/orangepi-r1-plus-lts-rk3328.scm (packages): Likewise.
* gnu/system/images/pine64.scm (packages): Likewise.
* gnu/system/install.scm (installation-os) [packages]: Likewise.

Change-Id: If09123a69b987178bcb0aab61c4570c14fc1286f

gnu/system/examples/vm-image.tmpl

@@ -7,7 +7,7 @@
 
 (use-modules (gnu) (guix) (srfi srfi-1))
 (use-service-modules desktop mcron networking spice ssh xorg sddm)
-(use-package-modules bootloaders certs fonts
+(use-package-modules bootloaders fonts
                      package-management xdisorg xorg)
 
 (define vm-image-motd (plain-file "motd" "
@@ -66,7 +66,7 @@ root ALL=(ALL) ALL
 %wheel ALL=NOPASSWD: ALL\n"))
 
   (packages
-   (append (list font-bitstream-vera nss-certs
+   (append (list font-bitstream-vera
                  ;; Auto-started script providing SPICE dynamic resizing for
                  ;; Xfce (see:
                  ;; https://gitlab.xfce.org/xfce/xfce4-settings/-/issues/142).