Fix warning

(cherry picked from commit 76cde63)

Author: nyalldawson

tests/src/core/testqgsmarkerlinesymbol.cpp

@@ -67,7 +67,6 @@ class TestQgsMarkerLineSymbol : public QObject
 
     QString mTestDataDir;
     QgsVectorLayer *mLinesLayer = nullptr;
-    QgsVectorLayer *mPolygonsLayer = nullptr;
     QgsMapSettings *mMapSettings = nullptr;
     QString mReport;
 };