[V0 deprecation] Deprecate V0 Neuron backend (#21159)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

vllm/model_executor/layers/activation.py

@@ -95,13 +95,6 @@ class SiluAndMul(CustomOp):
         self.op(out, x)
         return out
 
-    def forward_neuron(self, x: torch.Tensor) -> torch.Tensor:
-        d = x.shape[-1] // 2
-        x_reshaped = x.view(-1, x.shape[-1])
-        s = x_reshaped[:, :d] * F.sigmoid(x_reshaped[:, :d])
-        result = s * x_reshaped[:, d:]
-        return result.view(*x.shape[:-1], d)
-
 
 @CustomOp.register("mul_and_silu")
 class MulAndSilu(CustomOp):