__Current behavior before commit:__
When a sheet is deleted, `charts` from `OdooChartCorePlugin` are not
being updated.
Therefore, since the commit [`905d856`][1], `getOdooChartIds` returns
some chart ids that do not exist on any sheet anymore.
This induces a crash when opening a spreadsheet that contains such
charts.
__Description of the fix:__
Handle `DELETE_SHEET` event in `OdooChartCorePlugin` by removing Odoo
charts that don't belong to any sheet.
__Steps to reproduce the issue on runbot:__
- Insert a Odoo graph inside a spreadsheet (starting from any app)
- Add a sheet to it to the new spreadsheet
- Delete the sheet that contains the chart
- Leave the spreadsheet
- Go to Documents app and try to open the spreadsheet
-> Traceback
opw-3783745
[1]: https://github.com/odoo/odoo/commit/905d8565ad2fae3f7ff96606352ee3ab86ee78cbclosesodoo/odoo#157847
X-original-commit: d44c45234577d19a728e92368f224b0e0e59e853
Signed-off-by: Vincent Schippefilt (vsc) <vsc@odoo.com>