[FIX] account_asset_management: remove python-dateutil from depends

Such dependency is already included in Odoo requirements using a pinned
version [1]. Adding here could cause to upgrade the library to an
incompatible version.

[1] https://github.com/odoo/odoo/blob/1a264d7d9093/requirements.txt#L45

account_asset_management/__manifest__.py

@@ -10,7 +10,6 @@
     "depends": ["account", "report_xlsx_helper"],
     "excludes": ["account_asset"],
     "development_status": "Mature",
-    "external_dependencies": {"python": ["python-dateutil"]},
     "author": "Noviat, Odoo Community Association (OCA)",
     "website": "https://github.com/OCA/account-financial-tools",
     "category": "Accounting & Finance",

requirements.txt

@@ -2,5 +2,4 @@
 freezegun
 numpy-financial<=1.0.0
 numpy>=1.15
-python-dateutil
 vatnumber