Remove @FlakyTest on testTcpBufferReset

After aosp/1111617 merged, the test pass rate of
testTcpBufferReset is 100% on Android Test Metrics. That means
this test is not flaky. So remove @FlakyTest annotation on the
test.

Change-Id: I1fb47a9fda294030c41dc53cf4bac3849a2f3d54
Fix: 140305678
Test: atest ConnectivityServiceTest#testTcpBufferReset

tests/net/java/com/android/server/ConnectivityServiceTest.java

@@ -5696,7 +5696,6 @@ public class ConnectivityServiceTest {
     }
 
     @Test
-    @FlakyTest(bugId = 140305678)
     public void testTcpBufferReset() throws Exception {
         final String testTcpBufferSizes = "1,2,3,4,5,6";
         final NetworkRequest networkRequest = new NetworkRequest.Builder()