[core] Cleaned up TransitionOptions

include/mbgl/style/transition_options.hpp

@@ -6,13 +6,9 @@
 namespace mbgl {
 namespace style {
 
-class TransitionOptions {
-public:
-    TransitionOptions(optional<Duration> duration_ = {}, optional<Duration> delay_ = {})
-        : duration(std::move(duration_)), delay(std::move(delay_)) {}
-
-    optional<Duration> duration;
-    optional<Duration> delay;
+struct TransitionOptions {
+    optional<Duration> duration = {};
+    optional<Duration> delay = {};
 };
 
 } // namespace style

src/mbgl/style/cascade_parameters.hpp

@@ -9,8 +9,6 @@
 namespace mbgl {
 namespace style {
 
-class TransitionOptions;
-
 class CascadeParameters {
 public:
     std::vector<ClassID> classes;

src/mbgl/style/property_parsing.cpp

@@ -150,7 +150,7 @@ optional<TransitionOptions> parseTransitionOptions(const char *, const JSValue&
         return {};
     }
 
-    return TransitionOptions(duration, delay);
+    return TransitionOptions { duration, delay };
 }
 
 } // namespace style

src/mbgl/style/style.cpp

@@ -180,7 +180,7 @@ void Style::update(const UpdateParameters& parameters) {
 void Style::cascade(const TimePoint& timePoint, MapMode mode) {
     // When in continuous mode, we can either have user- or style-defined
     // transitions. Still mode is always immediate.
-    static const TransitionOptions immediateTransition;
+    static const TransitionOptions immediateTransition {};
 
     std::vector<ClassID> classIDs;
     for (const auto& className : classes) {