Flatpak: Remove leftover tenacity.desktop name

We have recently switched to rDNS schema. A little part was left out.

This change was merged ASAP, bypassing the normal review process,
because it is a follow up for a change that inadvertently resulted in
our Flatpak builds breaking.

Follow-up of 198d49b773.

Signed-off-by: TheEvilSkeleton <theevilskeleton@riseup.net>
Signed-off-by: Panagiotis Vasilopoulos <hello@alwayslivid.com>
Reference-to: https://github.com/tenacityteam/tenacity/pull/647

packaging/flatpak/org.tenacity.Tenacity.json

@@ -4,7 +4,6 @@
   "runtime-version": "40",
   "sdk": "org.gnome.Sdk",
   "command": "tenacity",
-  "rename-desktop-file": "tenacity.desktop",
   "rename-icon": "tenacity",
   "finish-args": [
     "--share=ipc",