doc: remove lttng from tierlist

PR-URL: #43604
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: tony-go

doc/contributing/diagnostic-tooling-support-tiers.md

@@ -134,7 +134,6 @@ The tools are currently assigned to Tiers as follows:
 | Debugger  | Command line Debug Client | ?                             | Yes                     | 1           |
 | Tracing   | trace\_events (API)       | No                            | Yes                     | 1           |
 | Tracing   | trace\_gc                 | No                            | Yes                     | 1           |
-| Tracing   | LTTng                     | No                            | Removed?                | N/A         |
 | Tracing   | Systemtap                 | No                            | Partial                 | ?           |
 | Profiling | Windows Xperf             | No                            | ?                       | ?           |
 | F/P/T     | appmetrics                | No                            | No                      | ?           |