udev: stop to use LOG_REALM_UDEV

Before this commit, udevd is built with LOG_REALM=LOG_REALM_UDEV.
However, log level specified by e.g. environment variable or kernel
command line option are also passed to LOG_REALM_SYSTEMD. So, the
maximum log level for the two realms are always equivalent, and it is
not necessary to specify the build option. Hence drop it.

src/test/meson.build

@@ -527,7 +527,7 @@ tests += [
           libkmod,
           libacl,
           libselinux],
-         udev_includes, '', 'manual', '-DLOG_REALM=LOG_REALM_UDEV'],
+         udev_includes, '', 'manual'],
 
         [['src/test/test-udev-util.c']],