Remove srtp_shutdown from res_srtp

The patch for ASTERISK-19253 included properly shutting down the libsrtp
library in the case of module unload.  Unfortunately, not all distributions
have the srtp_shutdown call.  As such, this patch removes calling
srtp_shutdown.
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Merged revisions 356650 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 356651 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@356652 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_srtp.c

@@ -530,9 +530,6 @@ static int ast_srtp_change_source(struct ast_srtp *srtp, unsigned int from_ssrc,
 static void res_srtp_shutdown(void)
 {
 	srtp_install_event_handler(NULL);
-	if (srtp_shutdown() != err_status_ok) {
-		ast_log(AST_LOG_WARNING, "Failed to de-initialize libsrtp\n");
-	}
 	ast_rtp_engine_unregister_srtp();
 	g_initialized = 0;
 }