Fix BF16 conv_transpose2d using wrong kernel on Metal (huggingface#3279)

* Changed CONVT1D_OP to CONVT2D_OP for conv_transpose2d_bf16

* removing the test: the cause of the bug is so apparent.

Author: amritsingh183

candle-metal-kernels/src/metal_src/conv.metal

@@ -713,5 +713,5 @@ CONVT1D_OP(bfloat, float, conv_transpose1d_bf16)
 CONVT2D_OP(float, float, conv_transpose2d_f32)
 CONVT2D_OP(half, float, conv_transpose2d_f16)
 #if defined(__HAVE_BFLOAT__)
-CONVT1D_OP(bfloat, float, conv_transpose2d_bf16)
+CONVT2D_OP(bfloat, float, conv_transpose2d_bf16)
 #endif