shader: Refactor PTP and other minor changes

src/shader_recompiler/frontend/ir/modifiers.h

@@ -32,11 +32,6 @@ struct FpControl {
 };
 static_assert(sizeof(FpControl) <= sizeof(u32));
 
-struct CompositeDecoration {
-    bool is_constant{false};
-};
-static_assert(sizeof(CompositeDecoration) <= sizeof(u32));
-
 union TextureInstInfo {
     u32 raw;
     BitField<0, 8, TextureType> type;