meson: drop explicit custom_target names

[1] says:
> Since 0.60.0 the name argument is optional and defaults to the basename of
> the first output
We specify >= 0.62 as the supported version, so drop the duplicate name in all cases
where it is the same as outputs[0], i.e. almost all cases.

[1] https://mesonbuild.com/Reference-manual_functions.html#custom_target

tmpfiles.d/meson.build

@@ -45,7 +45,6 @@ in_files = [
 foreach f : in_files
         if f.length() == 1 or conf.get(f[1]) == 1
                 custom_target(
-                        f[0],
                         input : f[0] + '.in',
                         output: f[0],
                         command : [jinja2_cmdline, '@INPUT@', '@OUTPUT@'],