GPU: remove 'GPU_SHADER_2D_IMAGE'

The only real difference between `GPU_SHADER_2D_IMAGE` and
`GPU_SHADER_3D_IMAGE` is that in the vertex shader the 2D
version uses `vec4(pos, 0.0, 1.0)` and the 3D version uses
`vec4(pos, 1.0)`.

But VBOs with 2D attributes work perfectly in shaders that use 3D
attributes. Components not specified are filled with components from
`vec4(0.0, 0.0, 0.0, 1.0)`.

So there is no real benefit to having two different shader versions.

This will simplify porting shaders to python as it will not be
necessary to use a 3D and a 2D version of the shaders.

In python the new name for '2D_IMAGE' and '3D_IMAGE'
is 'IMAGE', but the old names still work for backward
compatibility.

source/blender/gpu/shaders/infos/gpu_shader_2D_image_info.hh

@@ -16,8 +16,3 @@ GPU_SHADER_CREATE_INFO(gpu_shader_2D_image_common)
     .push_constant(Type::MAT4, "ModelViewProjectionMatrix")
     .sampler(0, ImageType::FLOAT_2D, "image")
     .vertex_source("gpu_shader_2D_image_vert.glsl");
-
-GPU_SHADER_CREATE_INFO(gpu_shader_2D_image)
-    .additional_info("gpu_shader_2D_image_common")
-    .fragment_source("gpu_shader_image_frag.glsl")
-    .do_static_compilation(true);