[Policy] Tricium-suggested cleanup

Change an empty destructor body to `= default'.

Change-Id: If1f3ce393aa45a93a806cf8336afddec070817ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2012543
Commit-Queue: Julian Pastarmov <pastarmovj@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Auto-Submit: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733973}

components/policy/core/common/configuration_policy_provider.cc

@@ -11,7 +11,7 @@
 
 namespace policy {
 
-ConfigurationPolicyProvider::Observer::~Observer() {}
+ConfigurationPolicyProvider::Observer::~Observer() = default;
 
 ConfigurationPolicyProvider::ConfigurationPolicyProvider()
     : initialized_(false), schema_registry_(nullptr) {}