[FIX] base_vat: greek vat number format

According to https://www.easytax.co/en/countries/greece
the vat number format for Greece is EL123456783
instead of GR12345670.
We also delete the line for country code `el`
from `_ref_vat` dict as we use `gr` for Greece.

opw-3845662

closes odoo/odoo#161955

X-original-commit: b97c74e43638d685b2af8ede4940f37b6a5cd031
Signed-off-by: Wala Gauthier (gawa) <gawa@odoo.com>
Signed-off-by: Guillaume Vanleynseele (guva) <guva@odoo.com>

addons/base_vat/models/res_partner.py

@@ -41,12 +41,11 @@ _ref_vat = {
     'do': _('DO1-01-85004-3 or 101850043'),
     'ec': _('1792060346001 or 1792060346'),
     'ee': 'EE123456780',
-    'el': 'EL12345670',
     'es': 'ESA12345674',
     'fi': 'FI12345671',
     'fr': 'FR23334175221',
     'gb': _('GB123456782 or XI123456782'),
-    'gr': 'GR12345670',
+    'gr': 'EL123456783',
     'hu': _('HU12345676 or 12345678-1-11 or 8071592153'),
     'hr': 'HR01234567896',  # Croatia, contributed by Milan Tribuson
     'ie': 'IE1234567FA',