Remove NetPrefObserver class and two prefs that do not do anything.

components/policy/resources/policy_templates.json

Index: components/policy/resources/policy_templates.json
diff --git a/components/policy/resources/policy_templates.json b/components/policy/resources/policy_templates.json
index 6279926f0370f03fde57967c76cc5a9f253f07d2..9c3d8067cb455c047e0fbe946cc3c317f71d9328 100644
--- a/components/policy/resources/policy_templates.json
+++ b/components/policy/resources/policy_templates.json
@@ -386,12 +386,13 @@
       'name': 'DnsPrefetchingEnabled',
       'type': 'main',
       'schema': { 'type': 'boolean' },
-      'supported_on': ['chrome.*:8-', 'chrome_os:11-', 'android:30-'],
+      'supported_on': ['chrome.*:8-53', 'chrome_os:11-53', 'android:30-53'],
       'features': {
         'can_be_recommended': True,
         'dynamic_refresh': True,
         'per_profile': True,
       },
+      'deprecated': True,
       'example_value': True,
       'id': 7,
       'caption': '''Enable network prediction''',
@@ -470,7 +471,7 @@
       'name': 'DisableSpdy',
       'type': 'main',
       'schema': { 'type': 'boolean' },
-      'supported_on': ['chrome.*:8-', 'chrome_os:11-', 'android:30-'],
+      'supported_on': ['chrome.*:8-53', 'chrome_os:11-53', 'android:30-53'],
       'features': {
         'dynamic_refresh': True,
         'per_profile': False,
@@ -480,7 +481,7 @@
       'id': 8,
       'caption': '''Disable SPDY protocol''',
       'tags': [],
-      'desc': '''This policy is deprecated, because SPDY/3.1 support is removed.
+      'desc': '''This policy is deprecated in M53 and removed in M54, because SPDY/3.1 support is removed.
 
       Disables use of the SPDY protocol in <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph>.