Delete cudnn6 code

Author: tianshuo78520a

paddle/fluid/platform/cudnn_helper.h

@@ -91,6 +91,22 @@ enum class ActivationMode {
   kBandPass,
 };
 
+inline cudnnPoolingMode_t GetPoolingMode(const PoolingMode& mode) {
+  switch (mode) {
+    case PoolingMode::kMaximumDeterministic:
+      return CUDNN_POOLING_MAX_DETERMINISTIC;
+    case PoolingMode::kAverageExclusive:
+      return CUDNN_POOLING_AVERAGE_COUNT_EXCLUDE_PADDING;
+    case PoolingMode::kAverageInclusive:
+      return CUDNN_POOLING_AVERAGE_COUNT_INCLUDE_PADDING;
+    case PoolingMode::kMaximum:
+      return CUDNN_POOLING_MAX;
+    default:
+      PADDLE_THROW(
+          platform::errors::Unimplemented("Unexpected CUDNN pooling mode."));
+  }
+}
+
 inline ActivationMode StringToActivationMode(const std::string& str) {
   if (str == "identity") {
     return ActivationMode::kNone;