[core] Inline TileSource::isRequired, remove unused isOptional

src/mbgl/tile/tile_source.hpp

@@ -44,14 +44,6 @@ class TileSource : private util::noncopyable {
     }
 
 private:
-    bool isOptional() const {
-        return necessity == Necessity::Optional;
-    }
-
-    bool isRequired() const {
-        return necessity == Necessity::Required;
-    }
-
     // called when the tile is one of the ideal tiles that we want to show definitely. the tile source
     // should try to make every effort (e.g. fetch from internet, or revalidate existing resources).
     void makeRequired();

src/mbgl/tile/tile_source_impl.hpp

@@ -34,7 +34,7 @@ TileSource<T>::TileSource(T& tileData_,
     } else {
         // When the FileSource doesn't support optional requests, we do nothing until the
         // data is definitely required.
-        if (isRequired()) {
+        if (necessity == Necessity::Required) {
             loadRequired();
         } else {
             // We're using this field to check whether the pending request is optional or required.
@@ -62,7 +62,7 @@ void TileSource<T>::loadOptional() {
             loadedData(res);
         }
 
-        if (isRequired()) {
+        if (necessity == Necessity::Required) {
             loadRequired();
         }
     });