[REM] web_diagram: remaining files

The web_diagram module was removed in saas-13.1,
along with the diagram view support but some translation files were
brought back by forwardports.

closes odoo/odoo#44563

X-original-commit: 3f50601736b23dac78720d24d5b67bf6b94f5f43
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>