meson: Remove -Wno-unused-parameter

We build libcamera with -Wno-unused-parameter and this doesn't cause
much issue internally. However, it prevents catching unused parameters
in inline functions defined in public headers. This can lead to
compilation warnings for applications compiled without
-Wno-unused-parameter.

To catch those issues, remove -Wno-unused-parameter and fix all the
related warnings with [[maybe_unused]].

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

test/libtest/test.h

@@ -30,7 +30,7 @@ protected:
 };
 
 #define TEST_REGISTER(klass)						\
-int main(int argc, char *argv[])					\
+int main([[maybe_unused]] int argc, [[maybe_unused]] char *argv[])	\
 {									\
 	return klass().execute();					\
 }