fix(http2): revert http2 refactor causing a client hang

This reverts commit 7b7dcc8f68.

tests/integration.rs

@@ -333,6 +333,9 @@ t! {
             ;
 }
 
+// In rare cases, the h2 client connection does not shutdown, resulting
+// in this test simply hanging... :(
+#[cfg(feature = "__internal_flaky_tests")]
 t! {
     http2_parallel_10,
     parallel: 0..10