In a project burndown chart, we currently have two measures, "Count" and "# of tasks".
Those measures are identical, but the default "Count" one is less explicit.
We only want to keep "# of tasks", but rather than discarding the default measure,
we could rename it and remove the other one.
This commit removes the "# of tasks" measure, and renames the default "Count"
into "# of tasks".
Task-2734458
closesodoo/odoo#86110
Related: odoo/upgrade#3357
Signed-off-by: Laurent Stukkens (ltu) <ltu@odoo.com>