Android: Fix Builderror due to unused tileCount variable

The Android build on CI failed with the following error
message:

../../qgroundcontrol/qgroundcontrol/src/QtLocationPlugin/QGCTileCacheWorker.cpp:510:21: error: variable 'tileCount' set but not used [-Werror,-Wunused-but-set-variable]
221
            quint64 tileCount = 0;

The tileCount variable is not used. I removed the variable.

src/QtLocationPlugin/QGCTileCacheWorker.cpp

@@ -507,13 +507,11 @@ QGCCacheWorker::_createTileSet(QGCMapTask *mtask)
             quint64 setID = query.lastInsertId().toULongLong();
             task->tileSet()->setId(setID);
             //-- Prepare Download List
-            quint64 tileCount = 0;
             _db->transaction();
             for(int z = task->tileSet()->minZoom(); z <= task->tileSet()->maxZoom(); z++) {
                 QGCTileSet set = QGCMapEngine::getTileCount(z,
                     task->tileSet()->topleftLon(), task->tileSet()->topleftLat(),
                     task->tileSet()->bottomRightLon(), task->tileSet()->bottomRightLat(), task->tileSet()->type());
-                tileCount += set.tileCount;
                 QString type = task->tileSet()->type();
                 for(int x = set.tileX0; x <= set.tileX1; x++) {
                     for(int y = set.tileY0; y <= set.tileY1; y++) {