core: cleanup header includes (#9088)

Cleanup some unneeded includes to speed up compilation

src/protocols/RelativePointer.cpp

@@ -1,5 +1,4 @@
 #include "RelativePointer.hpp"
-#include "../Compositor.hpp"
 #include "../managers/SeatManager.hpp"
 #include "core/Seat.hpp"
 #include <algorithm>
@@ -71,4 +70,4 @@ void CRelativePointerProtocol::sendRelativeMotion(uint64_t time, const Vector2D&
 
         rp->sendRelativeMotion(time, delta, deltaUnaccel);
     }
-}
+}