commands: delete obsolete include

This was removed in https://weave-review.googlesource.com/#/c/1788/

Change-Id: I7c1165c0e003cd7bb478555ac7886ed99d320615
Reviewed-on: https://weave-review.googlesource.com/1794
Reviewed-by: Alex Vakulenko <avakulenko@google.com>

src/commands/command_instance_unittest.cc

diff --git a/src/commands/command_instance_unittest.cc b/src/commands/command_instance_unittest.cc
index 6f55ad2..8d70b8b 100644
--- a/src/commands/command_instance_unittest.cc
+++ b/src/commands/command_instance_unittest.cc
@@ -7,8 +7,6 @@
 #include <gtest/gtest.h>
 #include <weave/test/unittest_utils.h>
 
-#include "src/commands/command_dictionary.h"
-
 namespace weave {
 
 using test::CreateDictionaryValue;