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/LibChess/UCICommand.cpp

@@ -316,9 +316,8 @@ String BestMoveCommand::to_string() const
     return builder.build();
 }
 
-InfoCommand InfoCommand::from_string(const StringView& command)
+InfoCommand InfoCommand::from_string([[maybe_unused]] const StringView& command)
 {
-    (void)command;
     // FIXME: Implement this.
     ASSERT_NOT_REACHED();
 }