man: sync up the suggested nsswitch.conf configuration for our four NSS modules

This unifies the suggested nsswitch.conf configuration for our four NSS modules to this:

    hosts: files mymachines resolve [!UNAVAIL=return] dns myhostname

Note that this restores "myhostname" to the suggested configuration of
nss-resolve for the time being, undoing 4484e1792b.

"myhostname" should probably be dropped eventually, but when we do this we
should do it in full, and not only drop it from the suggested nsswitch.conf
for one of the modules, but also drop it in source and stop referring to it
altogether.

Note that nss-resolve doesn't replace nss-myhostname in full: the former only
works if D-Bus/resolved is available for resolving the local hostname, the
latter works in all cases even if D-Bus or resolved are not in operation, hence
there's some value in keeping the line as it is right now. Note that neither
dns nor myhostname are considered at all with the above configuration unless
the resolve module actually returns UNAVAIL. Thus, even though handling of
local hostname resolving is implemented twice this way it is only executed once
for each lookup.

man/nss-myhostname.xml

@@ -110,7 +110,7 @@
 group:          compat mymachines systemd
 shadow:         compat
 
-hosts:          files mymachines resolve <command>myhostname</command>
+hosts:          files mymachines resolve [!UNAVAIL=return] dns <command>myhostname</command>
 networks:       files
 
 protocols:      db files

man/nss-mymachines.xml

@@ -86,7 +86,7 @@
 group:          compat <command>mymachines</command> systemd
 shadow:         compat
 
-hosts:          files <command>mymachines</command> resolve myhostname
+hosts:          files <command>mymachines</command> resolve [!UNAVAIL=return] dns myhostname
 networks:       files
 
 protocols:      db files

man/nss-resolve.xml

@@ -85,7 +85,7 @@
 group:          compat mymachines systemd
 shadow:         compat
 
-hosts:          files mymachines <command>resolve [!UNAVAIL=return]</command> dns
+hosts:          files mymachines <command>resolve [!UNAVAIL=return]</command> dns myhostname
 networks:       files
 
 protocols:      db files

man/nss-systemd.xml

@@ -83,7 +83,7 @@
 group:          compat mymachines <command>systemd</command>
 shadow:         compat
 
-hosts:          files mymachines resolve myhostname
+hosts:          files mymachines resolve [!UNAVAIL=return] dns myhostname
 networks:       files
 
 protocols:      db files