meson: do not explicitly specify ownership of /var/log/journal/

In 9289e093ae6fd5484f9119e1ee07d1dffe37cd10 we started using install_emptydir().

When running unprivileged, 'DESTDIR=… meson install -C build --quiet --no-rebuild'
would emit two warnings:
  '…/var/log/journal': Unable to set owner 'root' and group 'root': Operation not permitted, ignoring...
  '…/var/log/journal/remote': Unable to set owner 'root' and group 'root': Operation not permitted, ignoring...

Those were the only two install_emptydir()s that specified ownership.
Let's drop the user/group specification to get rid of the warning.

When installing as root, we will create a root-owned directory anyway.
When not running as root, we cannot create a root-owned directory.
So this specification only makes a difference if we are running as root,
and the directory already existed, and was not owned by root. In that case,
I think it's actually better to leave the existing modification in place.
(E.g. maybe the admin chgrp'ed the ownership for whatever reason. We might
just as well leave that in place.)

src/journal-remote/meson.build

@@ -114,6 +114,6 @@ if conf.get('ENABLE_REMOTE') == 1 and conf.get('HAVE_MICROHTTPD') == 1
 
         if get_option('create-log-dirs')
                 install_emptydir('/var/log/journal/remote',
-                                 install_mode : [ 'rwxr-xr-x', 'root', 'root' ])
+                                 install_mode : 'rwxr-xr-x')
         endif
 endif

src/journal/meson.build

@@ -185,7 +185,7 @@ endif
 
 if get_option('create-log-dirs')
         install_emptydir('/var/log/journal',
-                         install_mode : [ 'rwxr-xr-x', 'root', 'root' ])
+                         install_mode : 'rwxr-xr-x')
         if get_option('adm-group')
                 meson.add_install_script(
                         sh, '-c',