AsyncSSLSocketTest: Fix an LSAN error
AsyncSSLSocketTest: Fix an LSAN error

Summary:
SSLAcceptRunnerFiberCloseSessionCb was leaking the SSL_SESSION because it set a
custom server SSL session callback handler that did not properly manage the
SSL_SESSION that it was given.

Reviewed By: modiking

Differential Revision: D33807657

fbshipit-source-id: 5eeaecfef5df1f1d281abe2918f9926a969ab84d

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