Replace plane strings with literals (#6592)

Signed-off-by: Nick Cameron <nrc@ncameron.org>

public/kcl-samples/food-service-spatula/main.kcl

@@ -43,7 +43,7 @@ fn slot(sketch1, start, end, width) {
   return slotSketch
 }
 
-// Create a sketch on the "XY" plane for the flipper
+// Create a sketch on the XY plane for the flipper
 flipperSketch = startSketchOn(XY)
 
 // Create a profile of the flipper
@@ -82,7 +82,7 @@ fillet(
   ],
 )
 
-// Create a sketch on the "XZ" plane offset by half the thickness
+// Create a sketch on the XZ plane offset by half the thickness
 handleSketch = startSketchOn(offsetPlane(XZ, offset = -handleWidth / 2))
 
 // Create a profile of the spatula handle

public/kcl-samples/pipe-with-bend/main.kcl

@@ -10,7 +10,7 @@ outerDiameter = 20
 bendRadius = 30
 bendAngle = 90
 
-// Create a sketch in the 'XZ' plane
+// Create a sketch in the XZ plane
 sketch000 = startSketchOn(XZ)
 
 // Create a profile for the outer diameter