TUT: adjust surfaceFeatureExtractDict to remove optional sub-dictionary

- as of v1706
  extractFromSurfaceCoeffs { ... } is an optional subdictionary

tutorials/heatTransfer/chtMultiRegionFoam/snappyMultiRegionHeater/system/surfaceFeatureExtractDict

@@ -18,17 +18,15 @@ geom.stl
 {
     extractionMethod    extractFromSurface;
 
-    extractFromSurfaceCoeffs
-    {
-        // Mark edges whose adjacent surface normals are at an angle less
-        // than includedAngle as features
-        // - 0  : selects no edges
-        // - 180: selects all edges
-        includedAngle   150;
-    }
+    // Mark edges whose adjacent surface normals are at an angle less
+    // than includedAngle as features
+    // - 0  : selects no edges
+    // - 180: selects all edges
+    includedAngle       150;
 
     // Write options
     writeFeatureEdgeMesh    yes;
+
     // Write features to obj format for postprocessing
     writeObj                yes;
 }