Remove usages of IOBufQueue::clear()

Summary:
Drop all the remaining instances of `IOBufQueue::clear()`.

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum

Differential Revision: D32941992

fbshipit-source-id: c7d983e215a78014ffda74a944b628e1886c35c8

Author: ot

fizz/server/test/FizzServerTest.cpp

@@ -126,7 +126,7 @@ TEST_F(FizzServerTest, TestSSLV2AfterData) {
         return AsyncActions(Actions());
       }));
   fizzServer_->fizzServer_.newTransportData();
-  fizzServer_->queue_.clear();
+  fizzServer_->queue_.reset();
   fizzServer_->queue_.append(getV2ClientHello());
   EXPECT_CALL(
       *MockServerStateMachineInstance::instance, _processSocketData(_, _, _))