[AdgEntity] Removed adg_entity_ctm()

[AdgEntity] Removed adg_entity_ctm()

Getting rid of the ctm matrix from the cache as it is easy to get it by
combining the global and local matrix:

adg_matrix_copy(&ctm, global)
adg_matrix_transform(&ctm, local, ADG_TRANSFORM_BEFORE);

Furthermore, applying the ctm on a canvas with the global matrix
currently active (common inside the render callback) is trivial:

cairo_transform(cr, adg_entity_get_local_matrix(entity));