Everywhere: Switch from (void) to [[maybe_unused]] (#4473)

Problem:
- `(void)` simply casts the expression to void. This is understood to
  indicate that it is ignored, but this is really a compiler trick to
  get the compiler to not generate a warning.

Solution:
- Use the `[[maybe_unused]]` attribute to indicate the value is unused.

Note:
- Functions taking a `(void)` argument list have also been changed to
  `()` because this is not needed and shows up in the same grep
  command.

Libraries/LibC/syslog.cpp

@@ -94,7 +94,7 @@ void closelog_r(struct syslog_data* data)
     data->maskpri = LOG_UPTO(LOG_DEBUG);
 }
 
-void closelog(void)
+void closelog()
 {
     closelog_r(&global_log_data);
 }