meson: use install_emptydir() and drop meson-make-symlink.sh

The script is mostly equivalent to 'mkdir -p' and 'ln -sfr'.
Let's replace it with install_emptydir() builtin function and
inline meson call.

sysctl.d/meson.build

@@ -21,6 +21,5 @@ custom_target(
         install_dir : sysctldir)
 
 if install_sysconfdir
-        meson.add_install_script('sh', '-c',
-                                 mkdir_p.format(sysconfdir / 'sysctl.d'))
+        install_emptydir(sysconfdir / 'sysctl.d')
 endif