Remove eo_prefix

In this small example it is not necessary, so the tutorial is simpler.

tutorial/c/eo-classes/src/example_rectangle.eo

@@ -1,6 +1,5 @@
 class Example.Rectangle (Efl.Object, Example.Shape) {
    [[A rectangle shape object]]
-   eo_prefix: example_rectangle;
    methods {
       @property width {
          [[The width of this rectangle]]

tutorial/c/eo-classes/src/example_shape.eo

@@ -1,6 +1,5 @@
 interface Example.Shape {
    [[A generic shape object]]
-   eo_prefix: example_shape;
    methods {
       @property color {
          [[The colour that our shape should be filled with]]

tutorial/c/eo-classes/src/example_square.eo

@@ -1,6 +1,5 @@
 class Example.Square (Example.Rectangle) {
    [[A square shape object]]
-   eo_prefix: example_square;
    methods {
       @property side {
          [[The length of both sides of this square]]