[Mojo] Replace move implementations of MessageView with the default

The provided implementations are the same as the default, so just use
default.

Bug: None
Change-Id: Ie4c772a6371805cd869673b9979983cfa7714f29
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2249284Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Anand K Mistry <amistry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779563}

mojo/core/channel_fuchsia.cc

@@ -99,14 +99,9 @@ class MessageView {
     DCHECK_GT(message_->data_num_bytes(), offset_);
   }
 
-  MessageView(MessageView&& other) { *this = std::move(other); }
+  MessageView(MessageView&& other) = default;
 
-  MessageView& operator=(MessageView&& other) {
-    message_ = std::move(other.message_);
-    offset_ = other.offset_;
-    handles_ = std::move(other.handles_);
-    return *this;
-  }
+  MessageView& operator=(MessageView&& other) = default;
 
   ~MessageView() = default;
 

mojo/core/channel_posix.cc

@@ -47,7 +47,7 @@ class MessageView {
     DCHECK(!message_->data_num_bytes() || message_->data_num_bytes() > offset_);
   }
 
-  MessageView(MessageView&& other) { *this = std::move(other); }
+  MessageView(MessageView&& other) = default;
 
   MessageView& operator=(MessageView&& other) = default;