fix redundant initializations of Embeddings in RobertaEmbeddings
Based on the discussion with @julien-c in #1258, this PR fixes the issue of redundant multiple initializations of the embeddings in the constructor of `RobertaEmbeddings` by removing the constructor call of its parent class (i.e., `BertEmbeddings`) and creating `token_type_embeddings`, `LayerNorm`, and `dropout` in the constructor.
Sorry, I will fix this 