Cleanup: GPU: Remove GPU_draw_primitive and default_vao_

These are not used anymore and can be replicated using the GPUBatch API.

source/blender/gpu/opengl/gl_context.cc

@@ -47,8 +47,6 @@ using namespace blender::gpu;
 GLContext::GLContext(void *ghost_window, GLSharedOrphanLists &shared_orphan_list)
     : shared_orphan_list_(shared_orphan_list)
 {
-  glGenVertexArrays(1, &default_vao_);
-
   float data[4] = {0.0f, 0.0f, 0.0f, 1.0f};
   glGenBuffers(1, &default_attr_vbo_);
   glBindBuffer(GL_ARRAY_BUFFER, default_attr_vbo_);
@@ -101,7 +99,6 @@ GLContext::~GLContext()
   for (GLVaoCache *cache : vao_caches_) {
     cache->clear();
   }
-  glDeleteVertexArrays(1, &default_vao_);
   glDeleteBuffers(1, &default_attr_vbo_);
 }
 

source/blender/gpu/opengl/gl_context.hh

@@ -61,8 +61,6 @@ class GLSharedOrphanLists {
 class GLContext : public GPUContext {
   /* TODO(fclem) these needs to become private. */
  public:
-  /** Default VAO for procedural draw calls. */
-  GLuint default_vao_;
   /** VBO for missing vertex attrib binding. Avoid undefined behavior on some implementation. */
   GLuint default_attr_vbo_;
   /**