TUT: use general 'scale' instead of 'convertToMeters' in blockMeshDict

- although this has been supported for many years, the tutorials
  continued to use "convertToMeters" entry, which is specific to blockMesh.
  The "scale" is more consistent with other dictionaries.

ENH:
- ignore "scale 0;" (treat as no scaling) for blockMeshDict,
  consistent with use elsewhere.

tutorials/multiphase/multiphaseInterDyMFoam/laminar/mixerVesselAMI2D/system/blockMeshDict.m4

@@ -28,7 +28,7 @@ define(backQuad, ($1b $4b $3b $2b))
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-convertToMeters 0.1;
+scale   0.1;
 
 // Hub radius
 define(r, 0.2)