Remove duplicate code (#754)

Summary:
Remove duplicate definition of PositionalEmbedding in `lightconv.py`
Pull Request resolved: https://github.com/pytorch/fairseq/pull/754

Differential Revision: D15451443

Pulled By: myleott

fbshipit-source-id: a3d82ab2c1335d66be3c5d67a07893162d138c7a

fairseq/models/lightconv.py

@@ -23,10 +23,9 @@ from fairseq.modules import (
     AdaptiveSoftmax,
     DynamicConv1dTBC,
     LayerNorm,
-    LearnedPositionalEmbedding,
+    PositionalEmbedding,
     LightweightConv1dTBC,
     MultiheadAttention,
-    SinusoidalPositionalEmbedding,
 )
 
 
@@ -665,20 +664,6 @@ def Linear(in_features, out_features, bias=True):
     return m
 
 
-def PositionalEmbedding(num_embeddings, embedding_dim, padding_idx, learned=False):
-    if learned:
-        m = LearnedPositionalEmbedding(
-            num_embeddings + padding_idx + 1, embedding_dim, padding_idx,
-        )
-        nn.init.normal_(m.weight, mean=0, std=embedding_dim ** -0.5)
-        nn.init.constant_(m.weight[padding_idx], 0)
-    else:
-        m = SinusoidalPositionalEmbedding(
-            embedding_dim, padding_idx, init_size=num_embeddings + padding_idx + 1,
-        )
-    return m
-
-
 @register_model_architecture('lightconv', 'lightconv')
 def base_architecture(args):
     args.encoder_embed_path = getattr(args, 'encoder_embed_path', None)