simpler distilbert mask - fix tf tests

transformers/modeling_distilbert.py

@@ -159,8 +159,6 @@ class MultiHeadSelfAttention(nn.Module):
 
         dim_per_head = self.dim // self.n_heads
 
-        assert 2 <= mask.dim() <= 3
-        causal = (mask.dim() == 3)
         mask_reshp = (bs, 1, 1, k_length)
 
         def shape(x):

transformers/modeling_tf_distilbert.py

@@ -226,9 +226,6 @@ class TFMultiHeadSelfAttention(tf.keras.layers.Layer):
 
         dim_per_head = self.dim // self.n_heads
 
-        mask_shape = shape_list(mask)
-        assert 2 <= len(mask_shape) <= 3
-        causal = (mask_shape) == 3)
         mask_reshape = [bs, 1, 1, k_length]
 
         def shape(x):