Related to previous commit c07181b20b,
this commit fixed missed remplacments of this.env._t by _t, also
replace one occurence of _lt (not exist anymore) and replace remainings
core._t.
closes odoo/odoo#133503
Related: odoo/enterprise#46496
Signed-off-by: Michaël Mattiello (mcm) <mcm@odoo.com>