Reland "Cronet: add test server"

This reverts commit a0fdf1e70ea30b16c26f80143d8af9ed60c6b33f.

Reason for revert: Should work now after aosp/2314940
Also removes usage of the added test server

Test: atest CtsCronetTestCases
Change-Id: I1cde8ab8205c7ed12ce97ba6e9580c9b8c333053
diff --git a/Cronet/tests/cts/AndroidManifest.xml b/Cronet/tests/cts/AndroidManifest.xml
index 70acb0d..5a92dea 100644
--- a/Cronet/tests/cts/AndroidManifest.xml
+++ b/Cronet/tests/cts/AndroidManifest.xml
@@ -23,7 +23,7 @@
     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
 
-    <application android:usesCleartextTraffic="true">
+    <application android:networkSecurityConfig="@xml/network_security_config">
         <uses-library android:name="android.test.runner"/>
         <uses-library android:name="framework-cronet"/>
     </application>