[REF] *: get rid of vendor prefixes

BS4 do not provide vendor prefixes scss mixins anymore as it is meant
to be used with the 'autoprefixer' library. As we only support the last
version of every major browsers in Odoo, we took the decision to not
use the library as it was also complex to integrate in Odoo. We decided
to do the library's work by hand if it ever become necessary.