Change vertex buffer handling

Previously vertex data was only in shaders. I have removed it from there
and put hardcoded vertex data into cpp source code.

shaders/shader.frag

@@ -1,7 +1,6 @@
 #version 450
 
 layout(location = 0) in vec3 fragColor;
-
 layout(location = 0) out vec4 outColor;
 
 void main() {