Disable per-channel quant on requantize test (#2616)

BUG=cleanup

tensorflow/lite/micro/tools/requantize_flatbuffer_test.py

diff --git a/tensorflow/lite/micro/tools/requantize_flatbuffer_test.py b/tensorflow/lite/micro/tools/requantize_flatbuffer_test.py
index 342f893..885af89 100644
--- a/tensorflow/lite/micro/tools/requantize_flatbuffer_test.py
+++ b/tensorflow/lite/micro/tools/requantize_flatbuffer_test.py
@@ -62,6 +62,7 @@
   converter.representative_dataset = representative_dataset_gen
   # TODO(b/324385802): Support per-channel quantization for FullyConnected.
   converter._experimental_disable_per_channel_quantization_for_dense_layers = True
+  converter._experimental_disable_per_channel = True
   return converter.convert()