[REM] project: remove doc (#879)

This page documents a straightforward flow users can easily figure out without dedicated documentation. Besides, screens are frequently reworked, requiring to maintain the related page closely. This commit then removes a low-value page to reduce the technical debt and allow focusing on actually useful documentation pages.
Doc removed:
- forecast.rst

project.rst

@@ -8,4 +8,3 @@ Project
    :titlesonly:
 
    project/tasks
-   project/planning

project/planning.rst

@@ -1,8 +0,0 @@
-========
-Planning
-========
-
-.. toctree::
-   :titlesonly:
-
-   planning/forecast

project/planning/forecast.rst

@@ -1,47 +0,0 @@
-==================================
-Forecast Resources Across Projects
-==================================
-
-Allocate the needed time for specific tasks under a planned shift. Once that is done, analyse Key
-Performance Indicators (KPIs), so you can evaluate your employees’ performance and workload, besides
-the progress of your projects/tasks when comparing the planned and effective hours.
-
-Allocate times under shifts
-===========================
-
-When planning a shift, in the *Planning* application, create a project and a task on the fly,
-or simply select the one you want.
-
-.. image:: media/allocate_time.png
-   :align: center
-   :alt: Planning form to choose the project, task and allocated hours in Odoo Planning
-
-| *Allocated Time (%)* allows you to define the percentage of time you would like your employee to
-  work on that specific task during his shift. See that information in hours on *Allocated hours*.
-| The calculation shows you how many hours out of the total shift time (*End date* - *Start date*)
-  are spent by the employee on that task.
-| On :menuselection:`Project --> Planning --> By Project`, immediately see the total number of
-  employees allocated per project.
-
-.. image:: media/planning_project.png
-   :align: center
-   :alt: Planning by project view in Odoo Project
-
-Compare forecast hours with the effective ones
-==============================================
-
-Now, once the employee has timesheeted his hours in the task, go to *Project* and with the
-*View list*, under *All Tasks*, conveniently see the *Planned Hours* compared to the
-*Remaining Hours*, and a calculation of the *Progress*.
-
-.. image:: media/compare_forecast.png
-   :align: center
-   :alt: View of all tasks and their planned and remaining hours in Odoo Project
-
-.. important::
-   Reminder: the option *Timesheets* has to be enabled on your project.
-
-   .. image:: media/enable_timesheets.png
-      :align: center
-      :height: 400
-      :alt: Under the settings of a project enable timesheets in Odoo Project