meson: drop remaining target names

Most of those were dropped in 7d247d3cb8. I left
behind the few cases where the 'output' name was different from the target name.
But we actually don't need those either, so get rid of those. (And one case
where I missed the name argument.)

No functional change, except that e.g. 'ninja -C build update-man-rules-impl'
doesn't work, but I hope nobody was using that.

man/meson.build

@@ -217,7 +217,6 @@ configure_file(
 ############################################################
 
 update_dbus_docs = custom_target(
-        'update-dbus-docs-impl',
         output : 'update-dbus-docs',
         command : [update_dbus_docs_py, '--build-dir', meson.project_build_root(), '@INPUT@'],
         input : dbus_docs,
@@ -237,7 +236,6 @@ if conf.get('BUILD_MODE_DEVELOPER') == 1
 endif
 
 update_man_rules = custom_target(
-        'update-man-rules-impl',
         output : 'update-man-rules',
         command : [update_man_rules_py,
                    '@0@/man/*.xml'.format(meson.project_source_root()),

meson.build

@@ -2743,11 +2743,11 @@ foreach executable : ['systemd-journal-remote', 'systemd-sbsign', 'systemd-keyut
 endforeach
 
 if mkosi.found()
-        custom_target('mkosi',
+        custom_target(
                 build_always_stale : true,
                 build_by_default: false,
                 console : true,
-                output : '.',
+                output : 'mkosi',
                 command : [
                         mkosi,
                         '--directory', meson.current_source_dir(),

units/user/meson.build

@@ -82,7 +82,6 @@ foreach unit : units
 
         if needs_jinja
                 t = custom_target(
-                        name,
                         input : source,
                         output : name,
                         command : [jinja2_cmdline, '@INPUT@', '@OUTPUT@'],